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incorrect answer for limit involving erf #10976

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John-Colvin opened this Issue Apr 7, 2016 · 0 comments

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John-Colvin commented Apr 7, 2016

>>> import sympy as sy
>>> s, x = sy.symbols('s x', real=True)
>>> sy.limit(sy.erf(s*x)/sy.erf(s), s, 0)
1

The correct answer is x.

can be shown by l'Hopital's rule as follows:

image

Cross-checked with mathematica, see also http://www.wolframalpha.com/input/?i=lim_(s-%3E0)+(erf(s+x))%2F(erf(s))

skirpichev added a commit to diofant/diofant that referenced this issue Apr 7, 2016

Implement _erfs.eval helper
BTW, perhaps other cases of tractable functions
need some love, like this one.

Closes sympy/sympy#10976
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