[Python-checkins] Tweak polynomial itertool recipes (GH-102880)
rhettinger
webhook-mailer at python.org
Tue Mar 21 14:22:26 EDT 2023
https://github.com/python/cpython/commit/0214c7ad90b0afc3d1491c96e22e48d426caf5e2
commit: 0214c7ad90b0afc3d1491c96e22e48d426caf5e2
branch: main
author: Raymond Hettinger <rhettinger at users.noreply.github.com>
committer: rhettinger <rhettinger at users.noreply.github.com>
date: 2023-03-21T13:21:57-05:00
summary:
Tweak polynomial itertool recipes (GH-102880)
files:
M Doc/library/itertools.rst
diff --git a/Doc/library/itertools.rst b/Doc/library/itertools.rst
index 38bc369d410d..5daadfd3759f 100644
--- a/Doc/library/itertools.rst
+++ b/Doc/library/itertools.rst
@@ -866,6 +866,17 @@ which incur interpreter overhead.
window.append(x)
yield math.sumprod(kernel, window)
+ def polynomial_from_roots(roots):
+ """Compute a polynomial's coefficients from its roots.
+
+ (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)
+
def polynomial_eval(coefficients, x):
"""Evaluate a polynomial at a specific value.
@@ -876,20 +887,8 @@ which incur interpreter overhead.
n = len(coefficients)
if n == 0:
return x * 0 # coerce zero to the type of x
- powers = map(pow, repeat(x), range(n))
- return math.sumprod(reversed(coefficients), powers)
-
- def polynomial_from_roots(roots):
- """Compute a polynomial's coefficients from its roots.
-
- (x - 5) (x + 4) (x - 3) expands to: x³ -4x² -17x + 60
- """
- # polynomial_from_roots([5, -4, 3]) --> [1, -4, -17, 60]
- roots = list(map(operator.neg, roots))
- return [
- sum(map(math.prod, combinations(roots, k)))
- for k in range(len(roots) + 1)
- ]
+ powers = map(pow, repeat(x), reversed(range(n)))
+ return math.sumprod(coefficients, powers)
def iter_index(iterable, value, start=0):
"Return indices where a value occurs in a sequence or iterable."
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