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1494 lines
48 KiB
Python
1494 lines
48 KiB
Python
"""
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Objects for dealing with polynomials.
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This module provides a number of objects (mostly functions) useful for
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dealing with polynomials, including a `Polynomial` class that
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encapsulates the usual arithmetic operations. (General information
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on how this module represents and works with polynomial objects is in
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the docstring for its "parent" sub-package, `numpy.polynomial`).
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Constants
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---------
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- `polydomain` -- Polynomial default domain, [-1,1].
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- `polyzero` -- (Coefficients of the) "zero polynomial."
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- `polyone` -- (Coefficients of the) constant polynomial 1.
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- `polyx` -- (Coefficients of the) identity map polynomial, ``f(x) = x``.
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Arithmetic
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----------
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- `polyadd` -- add two polynomials.
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- `polysub` -- subtract one polynomial from another.
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- `polymulx` -- multiply a polynomial in ``P_i(x)`` by ``x``.
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- `polymul` -- multiply two polynomials.
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- `polydiv` -- divide one polynomial by another.
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- `polypow` -- raise a polynomial to a positive integer power.
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- `polyval` -- evaluate a polynomial at given points.
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- `polyval2d` -- evaluate a 2D polynomial at given points.
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- `polyval3d` -- evaluate a 3D polynomial at given points.
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- `polygrid2d` -- evaluate a 2D polynomial on a Cartesian product.
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- `polygrid3d` -- evaluate a 3D polynomial on a Cartesian product.
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Calculus
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--------
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- `polyder` -- differentiate a polynomial.
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- `polyint` -- integrate a polynomial.
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Misc Functions
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--------------
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- `polyfromroots` -- create a polynomial with specified roots.
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- `polyroots` -- find the roots of a polynomial.
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- `polyvalfromroots` -- evaluate a polynomial at given points from roots.
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- `polyvander` -- Vandermonde-like matrix for powers.
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- `polyvander2d` -- Vandermonde-like matrix for 2D power series.
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- `polyvander3d` -- Vandermonde-like matrix for 3D power series.
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- `polycompanion` -- companion matrix in power series form.
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- `polyfit` -- least-squares fit returning a polynomial.
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- `polytrim` -- trim leading coefficients from a polynomial.
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- `polyline` -- polynomial representing given straight line.
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Classes
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-------
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- `Polynomial` -- polynomial class.
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See Also
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--------
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`numpy.polynomial`
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"""
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from __future__ import division, absolute_import, print_function
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__all__ = [
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'polyzero', 'polyone', 'polyx', 'polydomain', 'polyline', 'polyadd',
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'polysub', 'polymulx', 'polymul', 'polydiv', 'polypow', 'polyval',
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'polyvalfromroots', 'polyder', 'polyint', 'polyfromroots', 'polyvander',
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'polyfit', 'polytrim', 'polyroots', 'Polynomial', 'polyval2d', 'polyval3d',
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'polygrid2d', 'polygrid3d', 'polyvander2d', 'polyvander3d']
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import warnings
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import numpy as np
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import numpy.linalg as la
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from numpy.core.multiarray import normalize_axis_index
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from . import polyutils as pu
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from ._polybase import ABCPolyBase
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polytrim = pu.trimcoef
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#
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# These are constant arrays are of integer type so as to be compatible
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# with the widest range of other types, such as Decimal.
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#
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# Polynomial default domain.
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polydomain = np.array([-1, 1])
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# Polynomial coefficients representing zero.
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polyzero = np.array([0])
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# Polynomial coefficients representing one.
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polyone = np.array([1])
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# Polynomial coefficients representing the identity x.
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polyx = np.array([0, 1])
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#
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# Polynomial series functions
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#
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def polyline(off, scl):
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"""
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Returns an array representing a linear polynomial.
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Parameters
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----------
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off, scl : scalars
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The "y-intercept" and "slope" of the line, respectively.
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Returns
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-------
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y : ndarray
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This module's representation of the linear polynomial ``off +
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scl*x``.
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See Also
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--------
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chebline
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Examples
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--------
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>>> from numpy.polynomial import polynomial as P
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>>> P.polyline(1,-1)
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array([ 1, -1])
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>>> P.polyval(1, P.polyline(1,-1)) # should be 0
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0.0
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"""
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if scl != 0:
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return np.array([off, scl])
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else:
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return np.array([off])
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def polyfromroots(roots):
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"""
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Generate a monic polynomial with given roots.
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Return the coefficients of the polynomial
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.. math:: p(x) = (x - r_0) * (x - r_1) * ... * (x - r_n),
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where the `r_n` are the roots specified in `roots`. If a zero has
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multiplicity n, then it must appear in `roots` n times. For instance,
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if 2 is a root of multiplicity three and 3 is a root of multiplicity 2,
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then `roots` looks something like [2, 2, 2, 3, 3]. The roots can appear
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in any order.
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If the returned coefficients are `c`, then
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.. math:: p(x) = c_0 + c_1 * x + ... + x^n
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The coefficient of the last term is 1 for monic polynomials in this
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form.
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Parameters
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----------
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roots : array_like
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Sequence containing the roots.
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Returns
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-------
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out : ndarray
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1-D array of the polynomial's coefficients If all the roots are
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real, then `out` is also real, otherwise it is complex. (see
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Examples below).
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See Also
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--------
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chebfromroots, legfromroots, lagfromroots, hermfromroots
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hermefromroots
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Notes
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-----
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The coefficients are determined by multiplying together linear factors
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of the form `(x - r_i)`, i.e.
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.. math:: p(x) = (x - r_0) (x - r_1) ... (x - r_n)
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where ``n == len(roots) - 1``; note that this implies that `1` is always
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returned for :math:`a_n`.
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Examples
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--------
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>>> from numpy.polynomial import polynomial as P
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>>> P.polyfromroots((-1,0,1)) # x(x - 1)(x + 1) = x^3 - x
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array([ 0., -1., 0., 1.])
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>>> j = complex(0,1)
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>>> P.polyfromroots((-j,j)) # complex returned, though values are real
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array([1.+0.j, 0.+0.j, 1.+0.j])
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"""
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return pu._fromroots(polyline, polymul, roots)
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def polyadd(c1, c2):
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"""
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Add one polynomial to another.
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Returns the sum of two polynomials `c1` + `c2`. The arguments are
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sequences of coefficients from lowest order term to highest, i.e.,
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[1,2,3] represents the polynomial ``1 + 2*x + 3*x**2``.
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Parameters
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----------
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c1, c2 : array_like
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1-D arrays of polynomial coefficients ordered from low to high.
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Returns
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-------
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out : ndarray
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The coefficient array representing their sum.
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See Also
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--------
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polysub, polymulx, polymul, polydiv, polypow
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Examples
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--------
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>>> from numpy.polynomial import polynomial as P
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>>> c1 = (1,2,3)
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>>> c2 = (3,2,1)
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>>> sum = P.polyadd(c1,c2); sum
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array([4., 4., 4.])
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>>> P.polyval(2, sum) # 4 + 4(2) + 4(2**2)
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28.0
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"""
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return pu._add(c1, c2)
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def polysub(c1, c2):
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"""
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Subtract one polynomial from another.
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Returns the difference of two polynomials `c1` - `c2`. The arguments
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are sequences of coefficients from lowest order term to highest, i.e.,
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[1,2,3] represents the polynomial ``1 + 2*x + 3*x**2``.
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Parameters
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----------
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c1, c2 : array_like
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1-D arrays of polynomial coefficients ordered from low to
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high.
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Returns
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-------
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out : ndarray
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Of coefficients representing their difference.
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See Also
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--------
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polyadd, polymulx, polymul, polydiv, polypow
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Examples
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--------
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>>> from numpy.polynomial import polynomial as P
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>>> c1 = (1,2,3)
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>>> c2 = (3,2,1)
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>>> P.polysub(c1,c2)
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array([-2., 0., 2.])
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>>> P.polysub(c2,c1) # -P.polysub(c1,c2)
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array([ 2., 0., -2.])
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"""
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return pu._sub(c1, c2)
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def polymulx(c):
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"""Multiply a polynomial by x.
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Multiply the polynomial `c` by x, where x is the independent
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variable.
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Parameters
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----------
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c : array_like
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1-D array of polynomial coefficients ordered from low to
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high.
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Returns
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-------
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out : ndarray
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Array representing the result of the multiplication.
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See Also
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--------
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polyadd, polysub, polymul, polydiv, polypow
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Notes
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-----
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.. versionadded:: 1.5.0
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"""
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# c is a trimmed copy
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[c] = pu.as_series([c])
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# The zero series needs special treatment
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if len(c) == 1 and c[0] == 0:
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return c
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prd = np.empty(len(c) + 1, dtype=c.dtype)
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prd[0] = c[0]*0
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prd[1:] = c
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return prd
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def polymul(c1, c2):
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"""
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Multiply one polynomial by another.
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Returns the product of two polynomials `c1` * `c2`. The arguments are
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sequences of coefficients, from lowest order term to highest, e.g.,
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[1,2,3] represents the polynomial ``1 + 2*x + 3*x**2.``
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Parameters
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----------
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c1, c2 : array_like
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1-D arrays of coefficients representing a polynomial, relative to the
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"standard" basis, and ordered from lowest order term to highest.
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Returns
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-------
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out : ndarray
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Of the coefficients of their product.
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See Also
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--------
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polyadd, polysub, polymulx, polydiv, polypow
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Examples
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--------
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>>> from numpy.polynomial import polynomial as P
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>>> c1 = (1,2,3)
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>>> c2 = (3,2,1)
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>>> P.polymul(c1,c2)
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array([ 3., 8., 14., 8., 3.])
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"""
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# c1, c2 are trimmed copies
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[c1, c2] = pu.as_series([c1, c2])
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ret = np.convolve(c1, c2)
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return pu.trimseq(ret)
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def polydiv(c1, c2):
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"""
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Divide one polynomial by another.
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Returns the quotient-with-remainder of two polynomials `c1` / `c2`.
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The arguments are sequences of coefficients, from lowest order term
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to highest, e.g., [1,2,3] represents ``1 + 2*x + 3*x**2``.
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Parameters
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----------
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c1, c2 : array_like
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1-D arrays of polynomial coefficients ordered from low to high.
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Returns
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-------
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[quo, rem] : ndarrays
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Of coefficient series representing the quotient and remainder.
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See Also
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--------
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polyadd, polysub, polymulx, polymul, polypow
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Examples
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--------
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>>> from numpy.polynomial import polynomial as P
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>>> c1 = (1,2,3)
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>>> c2 = (3,2,1)
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>>> P.polydiv(c1,c2)
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(array([3.]), array([-8., -4.]))
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>>> P.polydiv(c2,c1)
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(array([ 0.33333333]), array([ 2.66666667, 1.33333333])) # may vary
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"""
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# c1, c2 are trimmed copies
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[c1, c2] = pu.as_series([c1, c2])
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if c2[-1] == 0:
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raise ZeroDivisionError()
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# note: this is more efficient than `pu._div(polymul, c1, c2)`
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lc1 = len(c1)
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lc2 = len(c2)
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if lc1 < lc2:
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return c1[:1]*0, c1
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elif lc2 == 1:
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return c1/c2[-1], c1[:1]*0
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else:
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dlen = lc1 - lc2
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scl = c2[-1]
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c2 = c2[:-1]/scl
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i = dlen
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j = lc1 - 1
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while i >= 0:
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c1[i:j] -= c2*c1[j]
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i -= 1
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j -= 1
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return c1[j+1:]/scl, pu.trimseq(c1[:j+1])
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def polypow(c, pow, maxpower=None):
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"""Raise a polynomial to a power.
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Returns the polynomial `c` raised to the power `pow`. The argument
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`c` is a sequence of coefficients ordered from low to high. i.e.,
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[1,2,3] is the series ``1 + 2*x + 3*x**2.``
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Parameters
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----------
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c : array_like
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1-D array of array of series coefficients ordered from low to
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high degree.
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pow : integer
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Power to which the series will be raised
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maxpower : integer, optional
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Maximum power allowed. This is mainly to limit growth of the series
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to unmanageable size. Default is 16
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Returns
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-------
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coef : ndarray
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Power series of power.
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See Also
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--------
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polyadd, polysub, polymulx, polymul, polydiv
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Examples
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--------
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>>> from numpy.polynomial import polynomial as P
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>>> P.polypow([1,2,3], 2)
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array([ 1., 4., 10., 12., 9.])
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"""
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# note: this is more efficient than `pu._pow(polymul, c1, c2)`, as it
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# avoids calling `as_series` repeatedly
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return pu._pow(np.convolve, c, pow, maxpower)
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def polyder(c, m=1, scl=1, axis=0):
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"""
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Differentiate a polynomial.
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Returns the polynomial coefficients `c` differentiated `m` times along
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`axis`. At each iteration the result is multiplied by `scl` (the
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scaling factor is for use in a linear change of variable). The
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argument `c` is an array of coefficients from low to high degree along
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each axis, e.g., [1,2,3] represents the polynomial ``1 + 2*x + 3*x**2``
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while [[1,2],[1,2]] represents ``1 + 1*x + 2*y + 2*x*y`` if axis=0 is
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``x`` and axis=1 is ``y``.
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Parameters
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----------
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c : array_like
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Array of polynomial coefficients. If c is multidimensional the
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different axis correspond to different variables with the degree
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in each axis given by the corresponding index.
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m : int, optional
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Number of derivatives taken, must be non-negative. (Default: 1)
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scl : scalar, optional
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Each differentiation is multiplied by `scl`. The end result is
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multiplication by ``scl**m``. This is for use in a linear change
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of variable. (Default: 1)
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axis : int, optional
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Axis over which the derivative is taken. (Default: 0).
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|
|
.. versionadded:: 1.7.0
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Returns
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-------
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der : ndarray
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Polynomial coefficients of the derivative.
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|
See Also
|
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--------
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polyint
|
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|
|
Examples
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--------
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>>> from numpy.polynomial import polynomial as P
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>>> c = (1,2,3,4) # 1 + 2x + 3x**2 + 4x**3
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>>> P.polyder(c) # (d/dx)(c) = 2 + 6x + 12x**2
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array([ 2., 6., 12.])
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>>> P.polyder(c,3) # (d**3/dx**3)(c) = 24
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array([24.])
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>>> P.polyder(c,scl=-1) # (d/d(-x))(c) = -2 - 6x - 12x**2
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array([ -2., -6., -12.])
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>>> P.polyder(c,2,-1) # (d**2/d(-x)**2)(c) = 6 + 24x
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array([ 6., 24.])
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"""
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c = np.array(c, ndmin=1, copy=1)
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if c.dtype.char in '?bBhHiIlLqQpP':
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# astype fails with NA
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c = c + 0.0
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cdt = c.dtype
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cnt = pu._deprecate_as_int(m, "the order of derivation")
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iaxis = pu._deprecate_as_int(axis, "the axis")
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if cnt < 0:
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raise ValueError("The order of derivation must be non-negative")
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iaxis = normalize_axis_index(iaxis, c.ndim)
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if cnt == 0:
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return c
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c = np.moveaxis(c, iaxis, 0)
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n = len(c)
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if cnt >= n:
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c = c[:1]*0
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else:
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for i in range(cnt):
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n = n - 1
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c *= scl
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der = np.empty((n,) + c.shape[1:], dtype=cdt)
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for j in range(n, 0, -1):
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der[j - 1] = j*c[j]
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c = der
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c = np.moveaxis(c, 0, iaxis)
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return c
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def polyint(c, m=1, k=[], lbnd=0, scl=1, axis=0):
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"""
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Integrate a polynomial.
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|
Returns the polynomial coefficients `c` integrated `m` times from
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`lbnd` along `axis`. At each iteration the resulting series is
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**multiplied** by `scl` and an integration constant, `k`, is added.
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|
The scaling factor is for use in a linear change of variable. ("Buyer
|
|
beware": note that, depending on what one is doing, one may want `scl`
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|
to be the reciprocal of what one might expect; for more information,
|
|
see the Notes section below.) The argument `c` is an array of
|
|
coefficients, from low to high degree along each axis, e.g., [1,2,3]
|
|
represents the polynomial ``1 + 2*x + 3*x**2`` while [[1,2],[1,2]]
|
|
represents ``1 + 1*x + 2*y + 2*x*y`` if axis=0 is ``x`` and axis=1 is
|
|
``y``.
|
|
|
|
Parameters
|
|
----------
|
|
c : array_like
|
|
1-D array of polynomial coefficients, ordered from low to high.
|
|
m : int, optional
|
|
Order of integration, must be positive. (Default: 1)
|
|
k : {[], list, scalar}, optional
|
|
Integration constant(s). The value of the first integral at zero
|
|
is the first value in the list, the value of the second integral
|
|
at zero is the second value, etc. If ``k == []`` (the default),
|
|
all constants are set to zero. If ``m == 1``, a single scalar can
|
|
be given instead of a list.
|
|
lbnd : scalar, optional
|
|
The lower bound of the integral. (Default: 0)
|
|
scl : scalar, optional
|
|
Following each integration the result is *multiplied* by `scl`
|
|
before the integration constant is added. (Default: 1)
|
|
axis : int, optional
|
|
Axis over which the integral is taken. (Default: 0).
|
|
|
|
.. versionadded:: 1.7.0
|
|
|
|
Returns
|
|
-------
|
|
S : ndarray
|
|
Coefficient array of the integral.
|
|
|
|
Raises
|
|
------
|
|
ValueError
|
|
If ``m < 1``, ``len(k) > m``, ``np.ndim(lbnd) != 0``, or
|
|
``np.ndim(scl) != 0``.
|
|
|
|
See Also
|
|
--------
|
|
polyder
|
|
|
|
Notes
|
|
-----
|
|
Note that the result of each integration is *multiplied* by `scl`. Why
|
|
is this important to note? Say one is making a linear change of
|
|
variable :math:`u = ax + b` in an integral relative to `x`. Then
|
|
:math:`dx = du/a`, so one will need to set `scl` equal to
|
|
:math:`1/a` - perhaps not what one would have first thought.
|
|
|
|
Examples
|
|
--------
|
|
>>> from numpy.polynomial import polynomial as P
|
|
>>> c = (1,2,3)
|
|
>>> P.polyint(c) # should return array([0, 1, 1, 1])
|
|
array([0., 1., 1., 1.])
|
|
>>> P.polyint(c,3) # should return array([0, 0, 0, 1/6, 1/12, 1/20])
|
|
array([ 0. , 0. , 0. , 0.16666667, 0.08333333, # may vary
|
|
0.05 ])
|
|
>>> P.polyint(c,k=3) # should return array([3, 1, 1, 1])
|
|
array([3., 1., 1., 1.])
|
|
>>> P.polyint(c,lbnd=-2) # should return array([6, 1, 1, 1])
|
|
array([6., 1., 1., 1.])
|
|
>>> P.polyint(c,scl=-2) # should return array([0, -2, -2, -2])
|
|
array([ 0., -2., -2., -2.])
|
|
|
|
"""
|
|
c = np.array(c, ndmin=1, copy=1)
|
|
if c.dtype.char in '?bBhHiIlLqQpP':
|
|
# astype doesn't preserve mask attribute.
|
|
c = c + 0.0
|
|
cdt = c.dtype
|
|
if not np.iterable(k):
|
|
k = [k]
|
|
cnt = pu._deprecate_as_int(m, "the order of integration")
|
|
iaxis = pu._deprecate_as_int(axis, "the axis")
|
|
if cnt < 0:
|
|
raise ValueError("The order of integration must be non-negative")
|
|
if len(k) > cnt:
|
|
raise ValueError("Too many integration constants")
|
|
if np.ndim(lbnd) != 0:
|
|
raise ValueError("lbnd must be a scalar.")
|
|
if np.ndim(scl) != 0:
|
|
raise ValueError("scl must be a scalar.")
|
|
iaxis = normalize_axis_index(iaxis, c.ndim)
|
|
|
|
if cnt == 0:
|
|
return c
|
|
|
|
k = list(k) + [0]*(cnt - len(k))
|
|
c = np.moveaxis(c, iaxis, 0)
|
|
for i in range(cnt):
|
|
n = len(c)
|
|
c *= scl
|
|
if n == 1 and np.all(c[0] == 0):
|
|
c[0] += k[i]
|
|
else:
|
|
tmp = np.empty((n + 1,) + c.shape[1:], dtype=cdt)
|
|
tmp[0] = c[0]*0
|
|
tmp[1] = c[0]
|
|
for j in range(1, n):
|
|
tmp[j + 1] = c[j]/(j + 1)
|
|
tmp[0] += k[i] - polyval(lbnd, tmp)
|
|
c = tmp
|
|
c = np.moveaxis(c, 0, iaxis)
|
|
return c
|
|
|
|
|
|
def polyval(x, c, tensor=True):
|
|
"""
|
|
Evaluate a polynomial at points x.
|
|
|
|
If `c` is of length `n + 1`, this function returns the value
|
|
|
|
.. math:: p(x) = c_0 + c_1 * x + ... + c_n * x^n
|
|
|
|
The parameter `x` is converted to an array only if it is a tuple or a
|
|
list, otherwise it is treated as a scalar. In either case, either `x`
|
|
or its elements must support multiplication and addition both with
|
|
themselves and with the elements of `c`.
|
|
|
|
If `c` is a 1-D array, then `p(x)` will have the same shape as `x`. If
|
|
`c` is multidimensional, then the shape of the result depends on the
|
|
value of `tensor`. If `tensor` is true the shape will be c.shape[1:] +
|
|
x.shape. If `tensor` is false the shape will be c.shape[1:]. Note that
|
|
scalars have shape (,).
|
|
|
|
Trailing zeros in the coefficients will be used in the evaluation, so
|
|
they should be avoided if efficiency is a concern.
|
|
|
|
Parameters
|
|
----------
|
|
x : array_like, compatible object
|
|
If `x` is a list or tuple, it is converted to an ndarray, otherwise
|
|
it is left unchanged and treated as a scalar. In either case, `x`
|
|
or its elements must support addition and multiplication with
|
|
with themselves and with the elements of `c`.
|
|
c : array_like
|
|
Array of coefficients ordered so that the coefficients for terms of
|
|
degree n are contained in c[n]. If `c` is multidimensional the
|
|
remaining indices enumerate multiple polynomials. In the two
|
|
dimensional case the coefficients may be thought of as stored in
|
|
the columns of `c`.
|
|
tensor : boolean, optional
|
|
If True, the shape of the coefficient array is extended with ones
|
|
on the right, one for each dimension of `x`. Scalars have dimension 0
|
|
for this action. The result is that every column of coefficients in
|
|
`c` is evaluated for every element of `x`. If False, `x` is broadcast
|
|
over the columns of `c` for the evaluation. This keyword is useful
|
|
when `c` is multidimensional. The default value is True.
|
|
|
|
.. versionadded:: 1.7.0
|
|
|
|
Returns
|
|
-------
|
|
values : ndarray, compatible object
|
|
The shape of the returned array is described above.
|
|
|
|
See Also
|
|
--------
|
|
polyval2d, polygrid2d, polyval3d, polygrid3d
|
|
|
|
Notes
|
|
-----
|
|
The evaluation uses Horner's method.
|
|
|
|
Examples
|
|
--------
|
|
>>> from numpy.polynomial.polynomial import polyval
|
|
>>> polyval(1, [1,2,3])
|
|
6.0
|
|
>>> a = np.arange(4).reshape(2,2)
|
|
>>> a
|
|
array([[0, 1],
|
|
[2, 3]])
|
|
>>> polyval(a, [1,2,3])
|
|
array([[ 1., 6.],
|
|
[17., 34.]])
|
|
>>> coef = np.arange(4).reshape(2,2) # multidimensional coefficients
|
|
>>> coef
|
|
array([[0, 1],
|
|
[2, 3]])
|
|
>>> polyval([1,2], coef, tensor=True)
|
|
array([[2., 4.],
|
|
[4., 7.]])
|
|
>>> polyval([1,2], coef, tensor=False)
|
|
array([2., 7.])
|
|
|
|
"""
|
|
c = np.array(c, ndmin=1, copy=0)
|
|
if c.dtype.char in '?bBhHiIlLqQpP':
|
|
# astype fails with NA
|
|
c = c + 0.0
|
|
if isinstance(x, (tuple, list)):
|
|
x = np.asarray(x)
|
|
if isinstance(x, np.ndarray) and tensor:
|
|
c = c.reshape(c.shape + (1,)*x.ndim)
|
|
|
|
c0 = c[-1] + x*0
|
|
for i in range(2, len(c) + 1):
|
|
c0 = c[-i] + c0*x
|
|
return c0
|
|
|
|
|
|
def polyvalfromroots(x, r, tensor=True):
|
|
"""
|
|
Evaluate a polynomial specified by its roots at points x.
|
|
|
|
If `r` is of length `N`, this function returns the value
|
|
|
|
.. math:: p(x) = \\prod_{n=1}^{N} (x - r_n)
|
|
|
|
The parameter `x` is converted to an array only if it is a tuple or a
|
|
list, otherwise it is treated as a scalar. In either case, either `x`
|
|
or its elements must support multiplication and addition both with
|
|
themselves and with the elements of `r`.
|
|
|
|
If `r` is a 1-D array, then `p(x)` will have the same shape as `x`. If `r`
|
|
is multidimensional, then the shape of the result depends on the value of
|
|
`tensor`. If `tensor is ``True`` the shape will be r.shape[1:] + x.shape;
|
|
that is, each polynomial is evaluated at every value of `x`. If `tensor` is
|
|
``False``, the shape will be r.shape[1:]; that is, each polynomial is
|
|
evaluated only for the corresponding broadcast value of `x`. Note that
|
|
scalars have shape (,).
|
|
|
|
.. versionadded:: 1.12
|
|
|
|
Parameters
|
|
----------
|
|
x : array_like, compatible object
|
|
If `x` is a list or tuple, it is converted to an ndarray, otherwise
|
|
it is left unchanged and treated as a scalar. In either case, `x`
|
|
or its elements must support addition and multiplication with
|
|
with themselves and with the elements of `r`.
|
|
r : array_like
|
|
Array of roots. If `r` is multidimensional the first index is the
|
|
root index, while the remaining indices enumerate multiple
|
|
polynomials. For instance, in the two dimensional case the roots
|
|
of each polynomial may be thought of as stored in the columns of `r`.
|
|
tensor : boolean, optional
|
|
If True, the shape of the roots array is extended with ones on the
|
|
right, one for each dimension of `x`. Scalars have dimension 0 for this
|
|
action. The result is that every column of coefficients in `r` is
|
|
evaluated for every element of `x`. If False, `x` is broadcast over the
|
|
columns of `r` for the evaluation. This keyword is useful when `r` is
|
|
multidimensional. The default value is True.
|
|
|
|
Returns
|
|
-------
|
|
values : ndarray, compatible object
|
|
The shape of the returned array is described above.
|
|
|
|
See Also
|
|
--------
|
|
polyroots, polyfromroots, polyval
|
|
|
|
Examples
|
|
--------
|
|
>>> from numpy.polynomial.polynomial import polyvalfromroots
|
|
>>> polyvalfromroots(1, [1,2,3])
|
|
0.0
|
|
>>> a = np.arange(4).reshape(2,2)
|
|
>>> a
|
|
array([[0, 1],
|
|
[2, 3]])
|
|
>>> polyvalfromroots(a, [-1, 0, 1])
|
|
array([[-0., 0.],
|
|
[ 6., 24.]])
|
|
>>> r = np.arange(-2, 2).reshape(2,2) # multidimensional coefficients
|
|
>>> r # each column of r defines one polynomial
|
|
array([[-2, -1],
|
|
[ 0, 1]])
|
|
>>> b = [-2, 1]
|
|
>>> polyvalfromroots(b, r, tensor=True)
|
|
array([[-0., 3.],
|
|
[ 3., 0.]])
|
|
>>> polyvalfromroots(b, r, tensor=False)
|
|
array([-0., 0.])
|
|
"""
|
|
r = np.array(r, ndmin=1, copy=0)
|
|
if r.dtype.char in '?bBhHiIlLqQpP':
|
|
r = r.astype(np.double)
|
|
if isinstance(x, (tuple, list)):
|
|
x = np.asarray(x)
|
|
if isinstance(x, np.ndarray):
|
|
if tensor:
|
|
r = r.reshape(r.shape + (1,)*x.ndim)
|
|
elif x.ndim >= r.ndim:
|
|
raise ValueError("x.ndim must be < r.ndim when tensor == False")
|
|
return np.prod(x - r, axis=0)
|
|
|
|
|
|
def polyval2d(x, y, c):
|
|
"""
|
|
Evaluate a 2-D polynomial at points (x, y).
|
|
|
|
This function returns the value
|
|
|
|
.. math:: p(x,y) = \\sum_{i,j} c_{i,j} * x^i * y^j
|
|
|
|
The parameters `x` and `y` are converted to arrays only if they are
|
|
tuples or a lists, otherwise they are treated as a scalars and they
|
|
must have the same shape after conversion. In either case, either `x`
|
|
and `y` or their elements must support multiplication and addition both
|
|
with themselves and with the elements of `c`.
|
|
|
|
If `c` has fewer than two dimensions, ones are implicitly appended to
|
|
its shape to make it 2-D. The shape of the result will be c.shape[2:] +
|
|
x.shape.
|
|
|
|
Parameters
|
|
----------
|
|
x, y : array_like, compatible objects
|
|
The two dimensional series is evaluated at the points `(x, y)`,
|
|
where `x` and `y` must have the same shape. If `x` or `y` is a list
|
|
or tuple, it is first converted to an ndarray, otherwise it is left
|
|
unchanged and, if it isn't an ndarray, it is treated as a scalar.
|
|
c : array_like
|
|
Array of coefficients ordered so that the coefficient of the term
|
|
of multi-degree i,j is contained in `c[i,j]`. If `c` has
|
|
dimension greater than two the remaining indices enumerate multiple
|
|
sets of coefficients.
|
|
|
|
Returns
|
|
-------
|
|
values : ndarray, compatible object
|
|
The values of the two dimensional polynomial at points formed with
|
|
pairs of corresponding values from `x` and `y`.
|
|
|
|
See Also
|
|
--------
|
|
polyval, polygrid2d, polyval3d, polygrid3d
|
|
|
|
Notes
|
|
-----
|
|
|
|
.. versionadded:: 1.7.0
|
|
|
|
"""
|
|
return pu._valnd(polyval, c, x, y)
|
|
|
|
|
|
def polygrid2d(x, y, c):
|
|
"""
|
|
Evaluate a 2-D polynomial on the Cartesian product of x and y.
|
|
|
|
This function returns the values:
|
|
|
|
.. math:: p(a,b) = \\sum_{i,j} c_{i,j} * a^i * b^j
|
|
|
|
where the points `(a, b)` consist of all pairs formed by taking
|
|
`a` from `x` and `b` from `y`. The resulting points form a grid with
|
|
`x` in the first dimension and `y` in the second.
|
|
|
|
The parameters `x` and `y` are converted to arrays only if they are
|
|
tuples or a lists, otherwise they are treated as a scalars. In either
|
|
case, either `x` and `y` or their elements must support multiplication
|
|
and addition both with themselves and with the elements of `c`.
|
|
|
|
If `c` has fewer than two dimensions, ones are implicitly appended to
|
|
its shape to make it 2-D. The shape of the result will be c.shape[2:] +
|
|
x.shape + y.shape.
|
|
|
|
Parameters
|
|
----------
|
|
x, y : array_like, compatible objects
|
|
The two dimensional series is evaluated at the points in the
|
|
Cartesian product of `x` and `y`. If `x` or `y` is a list or
|
|
tuple, it is first converted to an ndarray, otherwise it is left
|
|
unchanged and, if it isn't an ndarray, it is treated as a scalar.
|
|
c : array_like
|
|
Array of coefficients ordered so that the coefficients for terms of
|
|
degree i,j are contained in ``c[i,j]``. If `c` has dimension
|
|
greater than two the remaining indices enumerate multiple sets of
|
|
coefficients.
|
|
|
|
Returns
|
|
-------
|
|
values : ndarray, compatible object
|
|
The values of the two dimensional polynomial at points in the Cartesian
|
|
product of `x` and `y`.
|
|
|
|
See Also
|
|
--------
|
|
polyval, polyval2d, polyval3d, polygrid3d
|
|
|
|
Notes
|
|
-----
|
|
|
|
.. versionadded:: 1.7.0
|
|
|
|
"""
|
|
return pu._gridnd(polyval, c, x, y)
|
|
|
|
|
|
def polyval3d(x, y, z, c):
|
|
"""
|
|
Evaluate a 3-D polynomial at points (x, y, z).
|
|
|
|
This function returns the values:
|
|
|
|
.. math:: p(x,y,z) = \\sum_{i,j,k} c_{i,j,k} * x^i * y^j * z^k
|
|
|
|
The parameters `x`, `y`, and `z` are converted to arrays only if
|
|
they are tuples or a lists, otherwise they are treated as a scalars and
|
|
they must have the same shape after conversion. In either case, either
|
|
`x`, `y`, and `z` or their elements must support multiplication and
|
|
addition both with themselves and with the elements of `c`.
|
|
|
|
If `c` has fewer than 3 dimensions, ones are implicitly appended to its
|
|
shape to make it 3-D. The shape of the result will be c.shape[3:] +
|
|
x.shape.
|
|
|
|
Parameters
|
|
----------
|
|
x, y, z : array_like, compatible object
|
|
The three dimensional series is evaluated at the points
|
|
`(x, y, z)`, where `x`, `y`, and `z` must have the same shape. If
|
|
any of `x`, `y`, or `z` is a list or tuple, it is first converted
|
|
to an ndarray, otherwise it is left unchanged and if it isn't an
|
|
ndarray it is treated as a scalar.
|
|
c : array_like
|
|
Array of coefficients ordered so that the coefficient of the term of
|
|
multi-degree i,j,k is contained in ``c[i,j,k]``. If `c` has dimension
|
|
greater than 3 the remaining indices enumerate multiple sets of
|
|
coefficients.
|
|
|
|
Returns
|
|
-------
|
|
values : ndarray, compatible object
|
|
The values of the multidimensional polynomial on points formed with
|
|
triples of corresponding values from `x`, `y`, and `z`.
|
|
|
|
See Also
|
|
--------
|
|
polyval, polyval2d, polygrid2d, polygrid3d
|
|
|
|
Notes
|
|
-----
|
|
|
|
.. versionadded:: 1.7.0
|
|
|
|
"""
|
|
return pu._valnd(polyval, c, x, y, z)
|
|
|
|
|
|
def polygrid3d(x, y, z, c):
|
|
"""
|
|
Evaluate a 3-D polynomial on the Cartesian product of x, y and z.
|
|
|
|
This function returns the values:
|
|
|
|
.. math:: p(a,b,c) = \\sum_{i,j,k} c_{i,j,k} * a^i * b^j * c^k
|
|
|
|
where the points `(a, b, c)` consist of all triples formed by taking
|
|
`a` from `x`, `b` from `y`, and `c` from `z`. The resulting points form
|
|
a grid with `x` in the first dimension, `y` in the second, and `z` in
|
|
the third.
|
|
|
|
The parameters `x`, `y`, and `z` are converted to arrays only if they
|
|
are tuples or a lists, otherwise they are treated as a scalars. In
|
|
either case, either `x`, `y`, and `z` or their elements must support
|
|
multiplication and addition both with themselves and with the elements
|
|
of `c`.
|
|
|
|
If `c` has fewer than three dimensions, ones are implicitly appended to
|
|
its shape to make it 3-D. The shape of the result will be c.shape[3:] +
|
|
x.shape + y.shape + z.shape.
|
|
|
|
Parameters
|
|
----------
|
|
x, y, z : array_like, compatible objects
|
|
The three dimensional series is evaluated at the points in the
|
|
Cartesian product of `x`, `y`, and `z`. If `x`,`y`, or `z` is a
|
|
list or tuple, it is first converted to an ndarray, otherwise it is
|
|
left unchanged and, if it isn't an ndarray, it is treated as a
|
|
scalar.
|
|
c : array_like
|
|
Array of coefficients ordered so that the coefficients for terms of
|
|
degree i,j are contained in ``c[i,j]``. If `c` has dimension
|
|
greater than two the remaining indices enumerate multiple sets of
|
|
coefficients.
|
|
|
|
Returns
|
|
-------
|
|
values : ndarray, compatible object
|
|
The values of the two dimensional polynomial at points in the Cartesian
|
|
product of `x` and `y`.
|
|
|
|
See Also
|
|
--------
|
|
polyval, polyval2d, polygrid2d, polyval3d
|
|
|
|
Notes
|
|
-----
|
|
|
|
.. versionadded:: 1.7.0
|
|
|
|
"""
|
|
return pu._gridnd(polyval, c, x, y, z)
|
|
|
|
|
|
def polyvander(x, deg):
|
|
"""Vandermonde matrix of given degree.
|
|
|
|
Returns the Vandermonde matrix of degree `deg` and sample points
|
|
`x`. The Vandermonde matrix is defined by
|
|
|
|
.. math:: V[..., i] = x^i,
|
|
|
|
where `0 <= i <= deg`. The leading indices of `V` index the elements of
|
|
`x` and the last index is the power of `x`.
|
|
|
|
If `c` is a 1-D array of coefficients of length `n + 1` and `V` is the
|
|
matrix ``V = polyvander(x, n)``, then ``np.dot(V, c)`` and
|
|
``polyval(x, c)`` are the same up to roundoff. This equivalence is
|
|
useful both for least squares fitting and for the evaluation of a large
|
|
number of polynomials of the same degree and sample points.
|
|
|
|
Parameters
|
|
----------
|
|
x : array_like
|
|
Array of points. The dtype is converted to float64 or complex128
|
|
depending on whether any of the elements are complex. If `x` is
|
|
scalar it is converted to a 1-D array.
|
|
deg : int
|
|
Degree of the resulting matrix.
|
|
|
|
Returns
|
|
-------
|
|
vander : ndarray.
|
|
The Vandermonde matrix. The shape of the returned matrix is
|
|
``x.shape + (deg + 1,)``, where the last index is the power of `x`.
|
|
The dtype will be the same as the converted `x`.
|
|
|
|
See Also
|
|
--------
|
|
polyvander2d, polyvander3d
|
|
|
|
"""
|
|
ideg = pu._deprecate_as_int(deg, "deg")
|
|
if ideg < 0:
|
|
raise ValueError("deg must be non-negative")
|
|
|
|
x = np.array(x, copy=0, ndmin=1) + 0.0
|
|
dims = (ideg + 1,) + x.shape
|
|
dtyp = x.dtype
|
|
v = np.empty(dims, dtype=dtyp)
|
|
v[0] = x*0 + 1
|
|
if ideg > 0:
|
|
v[1] = x
|
|
for i in range(2, ideg + 1):
|
|
v[i] = v[i-1]*x
|
|
return np.moveaxis(v, 0, -1)
|
|
|
|
|
|
def polyvander2d(x, y, deg):
|
|
"""Pseudo-Vandermonde matrix of given degrees.
|
|
|
|
Returns the pseudo-Vandermonde matrix of degrees `deg` and sample
|
|
points `(x, y)`. The pseudo-Vandermonde matrix is defined by
|
|
|
|
.. math:: V[..., (deg[1] + 1)*i + j] = x^i * y^j,
|
|
|
|
where `0 <= i <= deg[0]` and `0 <= j <= deg[1]`. The leading indices of
|
|
`V` index the points `(x, y)` and the last index encodes the powers of
|
|
`x` and `y`.
|
|
|
|
If ``V = polyvander2d(x, y, [xdeg, ydeg])``, then the columns of `V`
|
|
correspond to the elements of a 2-D coefficient array `c` of shape
|
|
(xdeg + 1, ydeg + 1) in the order
|
|
|
|
.. math:: c_{00}, c_{01}, c_{02} ... , c_{10}, c_{11}, c_{12} ...
|
|
|
|
and ``np.dot(V, c.flat)`` and ``polyval2d(x, y, c)`` will be the same
|
|
up to roundoff. This equivalence is useful both for least squares
|
|
fitting and for the evaluation of a large number of 2-D polynomials
|
|
of the same degrees and sample points.
|
|
|
|
Parameters
|
|
----------
|
|
x, y : array_like
|
|
Arrays of point coordinates, all of the same shape. The dtypes
|
|
will be converted to either float64 or complex128 depending on
|
|
whether any of the elements are complex. Scalars are converted to
|
|
1-D arrays.
|
|
deg : list of ints
|
|
List of maximum degrees of the form [x_deg, y_deg].
|
|
|
|
Returns
|
|
-------
|
|
vander2d : ndarray
|
|
The shape of the returned matrix is ``x.shape + (order,)``, where
|
|
:math:`order = (deg[0]+1)*(deg([1]+1)`. The dtype will be the same
|
|
as the converted `x` and `y`.
|
|
|
|
See Also
|
|
--------
|
|
polyvander, polyvander3d, polyval2d, polyval3d
|
|
|
|
"""
|
|
return pu._vander2d(polyvander, x, y, deg)
|
|
|
|
|
|
def polyvander3d(x, y, z, deg):
|
|
"""Pseudo-Vandermonde matrix of given degrees.
|
|
|
|
Returns the pseudo-Vandermonde matrix of degrees `deg` and sample
|
|
points `(x, y, z)`. If `l, m, n` are the given degrees in `x, y, z`,
|
|
then The pseudo-Vandermonde matrix is defined by
|
|
|
|
.. math:: V[..., (m+1)(n+1)i + (n+1)j + k] = x^i * y^j * z^k,
|
|
|
|
where `0 <= i <= l`, `0 <= j <= m`, and `0 <= j <= n`. The leading
|
|
indices of `V` index the points `(x, y, z)` and the last index encodes
|
|
the powers of `x`, `y`, and `z`.
|
|
|
|
If ``V = polyvander3d(x, y, z, [xdeg, ydeg, zdeg])``, then the columns
|
|
of `V` correspond to the elements of a 3-D coefficient array `c` of
|
|
shape (xdeg + 1, ydeg + 1, zdeg + 1) in the order
|
|
|
|
.. math:: c_{000}, c_{001}, c_{002},... , c_{010}, c_{011}, c_{012},...
|
|
|
|
and ``np.dot(V, c.flat)`` and ``polyval3d(x, y, z, c)`` will be the
|
|
same up to roundoff. This equivalence is useful both for least squares
|
|
fitting and for the evaluation of a large number of 3-D polynomials
|
|
of the same degrees and sample points.
|
|
|
|
Parameters
|
|
----------
|
|
x, y, z : array_like
|
|
Arrays of point coordinates, all of the same shape. The dtypes will
|
|
be converted to either float64 or complex128 depending on whether
|
|
any of the elements are complex. Scalars are converted to 1-D
|
|
arrays.
|
|
deg : list of ints
|
|
List of maximum degrees of the form [x_deg, y_deg, z_deg].
|
|
|
|
Returns
|
|
-------
|
|
vander3d : ndarray
|
|
The shape of the returned matrix is ``x.shape + (order,)``, where
|
|
:math:`order = (deg[0]+1)*(deg([1]+1)*(deg[2]+1)`. The dtype will
|
|
be the same as the converted `x`, `y`, and `z`.
|
|
|
|
See Also
|
|
--------
|
|
polyvander, polyvander3d, polyval2d, polyval3d
|
|
|
|
Notes
|
|
-----
|
|
|
|
.. versionadded:: 1.7.0
|
|
|
|
"""
|
|
return pu._vander3d(polyvander, x, y, z, deg)
|
|
|
|
|
|
def polyfit(x, y, deg, rcond=None, full=False, w=None):
|
|
"""
|
|
Least-squares fit of a polynomial to data.
|
|
|
|
Return the coefficients of a polynomial of degree `deg` that is the
|
|
least squares fit to the data values `y` given at points `x`. If `y` is
|
|
1-D the returned coefficients will also be 1-D. If `y` is 2-D multiple
|
|
fits are done, one for each column of `y`, and the resulting
|
|
coefficients are stored in the corresponding columns of a 2-D return.
|
|
The fitted polynomial(s) are in the form
|
|
|
|
.. math:: p(x) = c_0 + c_1 * x + ... + c_n * x^n,
|
|
|
|
where `n` is `deg`.
|
|
|
|
Parameters
|
|
----------
|
|
x : array_like, shape (`M`,)
|
|
x-coordinates of the `M` sample (data) points ``(x[i], y[i])``.
|
|
y : array_like, shape (`M`,) or (`M`, `K`)
|
|
y-coordinates of the sample points. Several sets of sample points
|
|
sharing the same x-coordinates can be (independently) fit with one
|
|
call to `polyfit` by passing in for `y` a 2-D array that contains
|
|
one data set per column.
|
|
deg : int or 1-D array_like
|
|
Degree(s) of the fitting polynomials. If `deg` is a single integer
|
|
all terms up to and including the `deg`'th term are included in the
|
|
fit. For NumPy versions >= 1.11.0 a list of integers specifying the
|
|
degrees of the terms to include may be used instead.
|
|
rcond : float, optional
|
|
Relative condition number of the fit. Singular values smaller
|
|
than `rcond`, relative to the largest singular value, will be
|
|
ignored. The default value is ``len(x)*eps``, where `eps` is the
|
|
relative precision of the platform's float type, about 2e-16 in
|
|
most cases.
|
|
full : bool, optional
|
|
Switch determining the nature of the return value. When ``False``
|
|
(the default) just the coefficients are returned; when ``True``,
|
|
diagnostic information from the singular value decomposition (used
|
|
to solve the fit's matrix equation) is also returned.
|
|
w : array_like, shape (`M`,), optional
|
|
Weights. If not None, the contribution of each point
|
|
``(x[i],y[i])`` to the fit is weighted by `w[i]`. Ideally the
|
|
weights are chosen so that the errors of the products ``w[i]*y[i]``
|
|
all have the same variance. The default value is None.
|
|
|
|
.. versionadded:: 1.5.0
|
|
|
|
Returns
|
|
-------
|
|
coef : ndarray, shape (`deg` + 1,) or (`deg` + 1, `K`)
|
|
Polynomial coefficients ordered from low to high. If `y` was 2-D,
|
|
the coefficients in column `k` of `coef` represent the polynomial
|
|
fit to the data in `y`'s `k`-th column.
|
|
|
|
[residuals, rank, singular_values, rcond] : list
|
|
These values are only returned if `full` = True
|
|
|
|
resid -- sum of squared residuals of the least squares fit
|
|
rank -- the numerical rank of the scaled Vandermonde matrix
|
|
sv -- singular values of the scaled Vandermonde matrix
|
|
rcond -- value of `rcond`.
|
|
|
|
For more details, see `linalg.lstsq`.
|
|
|
|
Raises
|
|
------
|
|
RankWarning
|
|
Raised if the matrix in the least-squares fit is rank deficient.
|
|
The warning is only raised if `full` == False. The warnings can
|
|
be turned off by:
|
|
|
|
>>> import warnings
|
|
>>> warnings.simplefilter('ignore', np.RankWarning)
|
|
|
|
See Also
|
|
--------
|
|
chebfit, legfit, lagfit, hermfit, hermefit
|
|
polyval : Evaluates a polynomial.
|
|
polyvander : Vandermonde matrix for powers.
|
|
linalg.lstsq : Computes a least-squares fit from the matrix.
|
|
scipy.interpolate.UnivariateSpline : Computes spline fits.
|
|
|
|
Notes
|
|
-----
|
|
The solution is the coefficients of the polynomial `p` that minimizes
|
|
the sum of the weighted squared errors
|
|
|
|
.. math :: E = \\sum_j w_j^2 * |y_j - p(x_j)|^2,
|
|
|
|
where the :math:`w_j` are the weights. This problem is solved by
|
|
setting up the (typically) over-determined matrix equation:
|
|
|
|
.. math :: V(x) * c = w * y,
|
|
|
|
where `V` is the weighted pseudo Vandermonde matrix of `x`, `c` are the
|
|
coefficients to be solved for, `w` are the weights, and `y` are the
|
|
observed values. This equation is then solved using the singular value
|
|
decomposition of `V`.
|
|
|
|
If some of the singular values of `V` are so small that they are
|
|
neglected (and `full` == ``False``), a `RankWarning` will be raised.
|
|
This means that the coefficient values may be poorly determined.
|
|
Fitting to a lower order polynomial will usually get rid of the warning
|
|
(but may not be what you want, of course; if you have independent
|
|
reason(s) for choosing the degree which isn't working, you may have to:
|
|
a) reconsider those reasons, and/or b) reconsider the quality of your
|
|
data). The `rcond` parameter can also be set to a value smaller than
|
|
its default, but the resulting fit may be spurious and have large
|
|
contributions from roundoff error.
|
|
|
|
Polynomial fits using double precision tend to "fail" at about
|
|
(polynomial) degree 20. Fits using Chebyshev or Legendre series are
|
|
generally better conditioned, but much can still depend on the
|
|
distribution of the sample points and the smoothness of the data. If
|
|
the quality of the fit is inadequate, splines may be a good
|
|
alternative.
|
|
|
|
Examples
|
|
--------
|
|
>>> np.random.seed(123)
|
|
>>> from numpy.polynomial import polynomial as P
|
|
>>> x = np.linspace(-1,1,51) # x "data": [-1, -0.96, ..., 0.96, 1]
|
|
>>> y = x**3 - x + np.random.randn(len(x)) # x^3 - x + N(0,1) "noise"
|
|
>>> c, stats = P.polyfit(x,y,3,full=True)
|
|
>>> np.random.seed(123)
|
|
>>> c # c[0], c[2] should be approx. 0, c[1] approx. -1, c[3] approx. 1
|
|
array([ 0.01909725, -1.30598256, -0.00577963, 1.02644286]) # may vary
|
|
>>> stats # note the large SSR, explaining the rather poor results
|
|
[array([ 38.06116253]), 4, array([ 1.38446749, 1.32119158, 0.50443316, # may vary
|
|
0.28853036]), 1.1324274851176597e-014]
|
|
|
|
Same thing without the added noise
|
|
|
|
>>> y = x**3 - x
|
|
>>> c, stats = P.polyfit(x,y,3,full=True)
|
|
>>> c # c[0], c[2] should be "very close to 0", c[1] ~= -1, c[3] ~= 1
|
|
array([-6.36925336e-18, -1.00000000e+00, -4.08053781e-16, 1.00000000e+00])
|
|
>>> stats # note the minuscule SSR
|
|
[array([ 7.46346754e-31]), 4, array([ 1.38446749, 1.32119158, # may vary
|
|
0.50443316, 0.28853036]), 1.1324274851176597e-014]
|
|
|
|
"""
|
|
return pu._fit(polyvander, x, y, deg, rcond, full, w)
|
|
|
|
|
|
def polycompanion(c):
|
|
"""
|
|
Return the companion matrix of c.
|
|
|
|
The companion matrix for power series cannot be made symmetric by
|
|
scaling the basis, so this function differs from those for the
|
|
orthogonal polynomials.
|
|
|
|
Parameters
|
|
----------
|
|
c : array_like
|
|
1-D array of polynomial coefficients ordered from low to high
|
|
degree.
|
|
|
|
Returns
|
|
-------
|
|
mat : ndarray
|
|
Companion matrix of dimensions (deg, deg).
|
|
|
|
Notes
|
|
-----
|
|
|
|
.. versionadded:: 1.7.0
|
|
|
|
"""
|
|
# c is a trimmed copy
|
|
[c] = pu.as_series([c])
|
|
if len(c) < 2:
|
|
raise ValueError('Series must have maximum degree of at least 1.')
|
|
if len(c) == 2:
|
|
return np.array([[-c[0]/c[1]]])
|
|
|
|
n = len(c) - 1
|
|
mat = np.zeros((n, n), dtype=c.dtype)
|
|
bot = mat.reshape(-1)[n::n+1]
|
|
bot[...] = 1
|
|
mat[:, -1] -= c[:-1]/c[-1]
|
|
return mat
|
|
|
|
|
|
def polyroots(c):
|
|
"""
|
|
Compute the roots of a polynomial.
|
|
|
|
Return the roots (a.k.a. "zeros") of the polynomial
|
|
|
|
.. math:: p(x) = \\sum_i c[i] * x^i.
|
|
|
|
Parameters
|
|
----------
|
|
c : 1-D array_like
|
|
1-D array of polynomial coefficients.
|
|
|
|
Returns
|
|
-------
|
|
out : ndarray
|
|
Array of the roots of the polynomial. If all the roots are real,
|
|
then `out` is also real, otherwise it is complex.
|
|
|
|
See Also
|
|
--------
|
|
chebroots
|
|
|
|
Notes
|
|
-----
|
|
The root estimates are obtained as the eigenvalues of the companion
|
|
matrix, Roots far from the origin of the complex plane may have large
|
|
errors due to the numerical instability of the power series for such
|
|
values. Roots with multiplicity greater than 1 will also show larger
|
|
errors as the value of the series near such points is relatively
|
|
insensitive to errors in the roots. Isolated roots near the origin can
|
|
be improved by a few iterations of Newton's method.
|
|
|
|
Examples
|
|
--------
|
|
>>> import numpy.polynomial.polynomial as poly
|
|
>>> poly.polyroots(poly.polyfromroots((-1,0,1)))
|
|
array([-1., 0., 1.])
|
|
>>> poly.polyroots(poly.polyfromroots((-1,0,1))).dtype
|
|
dtype('float64')
|
|
>>> j = complex(0,1)
|
|
>>> poly.polyroots(poly.polyfromroots((-j,0,j)))
|
|
array([ 0.00000000e+00+0.j, 0.00000000e+00+1.j, 2.77555756e-17-1.j]) # may vary
|
|
|
|
"""
|
|
# c is a trimmed copy
|
|
[c] = pu.as_series([c])
|
|
if len(c) < 2:
|
|
return np.array([], dtype=c.dtype)
|
|
if len(c) == 2:
|
|
return np.array([-c[0]/c[1]])
|
|
|
|
# rotated companion matrix reduces error
|
|
m = polycompanion(c)[::-1,::-1]
|
|
r = la.eigvals(m)
|
|
r.sort()
|
|
return r
|
|
|
|
|
|
#
|
|
# polynomial class
|
|
#
|
|
|
|
class Polynomial(ABCPolyBase):
|
|
"""A power series class.
|
|
|
|
The Polynomial class provides the standard Python numerical methods
|
|
'+', '-', '*', '//', '%', 'divmod', '**', and '()' as well as the
|
|
attributes and methods listed in the `ABCPolyBase` documentation.
|
|
|
|
Parameters
|
|
----------
|
|
coef : array_like
|
|
Polynomial coefficients in order of increasing degree, i.e.,
|
|
``(1, 2, 3)`` give ``1 + 2*x + 3*x**2``.
|
|
domain : (2,) array_like, optional
|
|
Domain to use. The interval ``[domain[0], domain[1]]`` is mapped
|
|
to the interval ``[window[0], window[1]]`` by shifting and scaling.
|
|
The default value is [-1, 1].
|
|
window : (2,) array_like, optional
|
|
Window, see `domain` for its use. The default value is [-1, 1].
|
|
|
|
.. versionadded:: 1.6.0
|
|
|
|
"""
|
|
# Virtual Functions
|
|
_add = staticmethod(polyadd)
|
|
_sub = staticmethod(polysub)
|
|
_mul = staticmethod(polymul)
|
|
_div = staticmethod(polydiv)
|
|
_pow = staticmethod(polypow)
|
|
_val = staticmethod(polyval)
|
|
_int = staticmethod(polyint)
|
|
_der = staticmethod(polyder)
|
|
_fit = staticmethod(polyfit)
|
|
_line = staticmethod(polyline)
|
|
_roots = staticmethod(polyroots)
|
|
_fromroots = staticmethod(polyfromroots)
|
|
|
|
# Virtual properties
|
|
nickname = 'poly'
|
|
domain = np.array(polydomain)
|
|
window = np.array(polydomain)
|
|
basis_name = None
|
|
|
|
@staticmethod
|
|
def _repr_latex_term(i, arg_str, needs_parens):
|
|
if needs_parens:
|
|
arg_str = r'\left({}\right)'.format(arg_str)
|
|
if i == 0:
|
|
return '1'
|
|
elif i == 1:
|
|
return arg_str
|
|
else:
|
|
return '{}^{{{}}}'.format(arg_str, i)
|