Skip to content

Update itertool recipe: polynomial_from_roots() #103973

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 2 commits into from
Apr 28, 2023
Merged

Update itertool recipe: polynomial_from_roots() #103973

Changes from all commits
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
ac1fb7a
Functional version that better demonstrates iterator chaining
rhettinger Apr 28, 2023
95ab9e3
Be consistent with use of repeat().
rhettinger Apr 28, 2023
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
9 changes: 4 additions & 5 deletions Doc/library/itertools.rst
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -789,6 +789,7 @@ which incur interpreter overhead.
.. testcode::

import collections
import functools
import math
import operator
import random
Expand Down Expand Up @@ -1082,7 +1083,7 @@ The following recipes have a more mathematical flavor:
# convolve(data, [1, -2, 1]) --> 2nd finite difference (2nd derivative)
kernel = tuple(kernel)[::-1]
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):
yield math.sumprod(kernel, window)

Expand All @@ -1092,10 +1093,8 @@ The following recipes have a more mathematical flavor:
(x - 5) (x + 4) (x - 3) expands to: x³ -4x² -17x + 60
"""
# polynomial_from_roots([5, -4, 3]) --> [1, -4, -17, 60]
expansion = [1]
for r in roots:
expansion = convolve(expansion, (1, -r))
return list(expansion)
factors = zip(repeat(1), map(operator.neg, roots))
return list(functools.reduce(convolve, factors, [1]))

def polynomial_eval(coefficients, x):
"""Evaluate a polynomial at a specific value.
Expand Down