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Update itertool recipe: polynomial_from_roots() (GH-103973)

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Raymond Hettinger 2023-04-28 12:25:50 -05:00 committed by GitHub
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commit c3453fbb11
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1 changed files with 4 additions and 5 deletions
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Doc/library/itertools.rst
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@ -789,6 +789,7 @@ which incur interpreter overhead.
.. testcode:: .. testcode::
import collections import collections
import functools
import math import math
import operator import operator
import random import random
@ -1082,7 +1083,7 @@ The following recipes have a more mathematical flavor:
# convolve(data, [1, -2, 1]) --> 2nd finite difference (2nd derivative) # convolve(data, [1, -2, 1]) --> 2nd finite difference (2nd derivative)
kernel = tuple(kernel)[::-1] kernel = tuple(kernel)[::-1]
n = len(kernel) n = len(kernel)
padded_signal = chain(repeat(0, n-1), signal, [0] * (n-1)) padded_signal = chain(repeat(0, n-1), signal, repeat(0, n-1))
for window in sliding_window(padded_signal, n): for window in sliding_window(padded_signal, n):
yield math.sumprod(kernel, window) yield math.sumprod(kernel, window)
@ -1092,10 +1093,8 @@ The following recipes have a more mathematical flavor:
(x - 5) (x + 4) (x - 3) expands to: x³ -4x² -17x + 60 (x - 5) (x + 4) (x - 3) expands to: x³ -4x² -17x + 60
""" """
# polynomial_from_roots([5, -4, 3]) --> [1, -4, -17, 60] # polynomial_from_roots([5, -4, 3]) --> [1, -4, -17, 60]
expansion = [1] factors = zip(repeat(1), map(operator.neg, roots))
for r in roots: return list(functools.reduce(convolve, factors, [1]))
expansion = convolve(expansion, (1, -r))
return list(expansion)
def polynomial_eval(coefficients, x): def polynomial_eval(coefficients, x):
"""Evaluate a polynomial at a specific value. """Evaluate a polynomial at a specific value.