Thanks for replying.

On Sat, Dec 1, 2012 at 8:49 AM, Aaron Meurer <[email protected]> wrote:
>
> easy way to fix it is to use summation(t**i*Ra(i),(i,0,5)).doit().

Wow nice, that works!

> Care to open an issue for this in our issue tracker
> (https://code.google.com/p/sympy/issues/list)?

I reported it here with your comments:
https://code.google.com/p/sympy/issues/detail?id=3543

Note that I have made the subject to read "summation containing
summation" but perhaps the actual bug is more widespread than that so
please change the title if inappropriate or inaccurate.

On Sat, Dec 1, 2012 at 8:30 AM, Shriramana Sharma <[email protected]> wrote:
> print(summation(t**i*Ra(i),(i,0,5)))

Curiously replacing 5 by n, i.e. as
print(summation(t**i*Ra(i),(i,0,n))) gives the output:

Sum(t**i*Sum((-1)**(i + j)*ival(j)*binomial(i, j)*binomial(n, i), (j,
0, i)), (i, 0, n))

so only when the actual finite evaluation is done does the problem surface.

-- 
Shriramana Sharma

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