Re: [Reduce-algebra-developers] expansion of gamma function

[Alan B. <ala...@gm...>]

I note that the taylor package also fails on this example.

the tps package basically differentiates repeatedly the function to be 
expanded and tries to build a recurrence relation for the terms of the 
series and also tries to work out the value of the lowest term in the 
series.

It looks as if this process generates a call to an undefined function 
namely polygamma_aux probably when it is attempting to evaluate the 
function at x=0.

  Without looking at the code it appears that repeated differentiation 
of gamma will generate an infinite sequence of polygammas with their 
first argument increasing by 1 at each stage and it is hard to see how 
this will process will close.

I will try to look at the problem in the next week or so.

Alan Barnes

On 09/10/2015 18:32, gr...@ge... wrote:
> grozin@dns ~/reduce-3235 $ bin/rfpsl
> Redfront 3.2, built 09-Oct-2015 ...
> Loading image file:
> /home/grozin/reduce-3235/pslbuild/x86_64-unknown-gentoo2.2/red/reduce.img
>
> Reduce (Free PSL version),  9-Oct-2015 ...
>
> 1: load_package specfn;
>
> 2: load_package tps;
>
> 3: psexplim 5$
>
> 4: ps(gamma(1+x),x,0);
> ***** `polygamma_aux' is an undefined function
>
> 5:
>
> What can polygamma_aux be?
> I seem to remember that in elder days this expansion worked (though maybe
> I'm wrong).
>
> Andrey
>
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