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Behavior of symbolic_sum changed?

asked 2017-08-11 12:56:28 -0500

Peter Luschny gravatar image

Consider

from sage.calculus.calculus import symbolic_sum
n = var('n')
print 1/(1 + symbolic_sum(factorial(n) * x^n, n, 1, oo))

Answer of Sage 7.4:

1/(x*hypergeometric((1, 2), (), x) + 1)

Answer of Sage 8.0:

ValueError: Computation failed since Maxima requested 
additional constraints; ....
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answered 2017-08-11 14:44:00 -0500

Richard_L gravatar image

updated 2017-08-11 15:59:14 -0500

Expand the traceback. You'll see that "assume ... may help" (or words to that effect). Indeed:

from sage.calculus.calculus import symbolic_sum
n = var('n')
var('x'); assume(x==0)
print 1/(1 + symbolic_sum(factorial(n) * x^n, n, 1, oo))

gives the answer you got in 7.4:

1/(x*hypergeometric((1, 2), (), x) + 1)

However, if we assume (x>0) or assume (x<0), we get "Sum divergent".

The short answer: Maxima was up-rev'd with sage-8.0 to maxima-5.39.0 and may exhibit different behavior from previous versions.

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Asked: 2017-08-11 12:56:28 -0500

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Last updated: Aug 11