Hello,
while working on a ticket I encountered different behaviour of python sum
in Sage regarding whether the sum (over a symbolic expression applied to a
range)
was given on the command line vs. in Sage-lib (python file) within a
function definition.
Specifically, applying this one-line patch on top of develop:
diff --git a/src/sage/rings/arith.py b/src/sage/rings/arith.py
--- a/src/sage/rings/arith.py
+++ b/src/sage/rings/arith.py
@@ -5336,6 +5336,7 @@ def subfactorial(n):
- Jaap Spies (2007-01-23)
"""
+ from sage.functions.other import factorial
return factorial(n)*sum(((-1)**k)/factorial(k) for k in range(n+1))
will show on the command line:
sage: subfactorial(8)
-120960
which is wrong but when I define the same function there:
sage: from sage.functions.other import factorial
sage: def subf(n):
return factorial(n)*sum(((-1)**k)/factorial(k) for k in range(n+1))
....:
sage: subf(8)
14833
This effect only happens with Python sum/prod. So, what difference does
using Python sum/prod on the command line make vs. in a py file?
Please help,
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