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Some wrong answers from rsolve #11063

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asmeurer opened this Issue Apr 29, 2016 · 0 comments

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asmeurer commented Apr 29, 2016

From https://stackoverflow.com/questions/36905146/is-it-possible-to-find-the-close-form-solution-of-following-recurrence-relation

>>> from sympy import *
>>> F=Function('F')
>>> t=symbol('t')
>>> n=Symbol('n')
>>> f=F(n+1,t)-F(n,2*t)
>>> rsolve(f,F(n,t),{F(0,t):t})
t
>>> y=Symbol('y')
>>> f=F(n+1,y,t)-F(n,y+1,y*t)
>>> rsolve(f,F(n,y,t),{F(0,y,t):t})
t 

Both answers are wrong (the correct answers are 2**n*t and t*rf(y, n+1)). A simple substitution in each case shows that t isn't even right as a trivial solution.

skirpichev added a commit to diofant/diofant that referenced this issue Apr 30, 2016

skirpichev added a commit to skirpichev/diofant that referenced this issue May 13, 2016

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