# [Maxima] Matrices of indefinite size

Richard Fateman fateman at cs.berkeley.edu
Tue Mar 18 23:17:37 CDT 2008

```That is exactly the correct answer, and is computed by maxima and macsyma.

when you replaced "mysum" by "sum" the proof doesn't work.   mysum knows

RJF

> -----Original Message-----
> From: maxima-bounces at math.utexas.edu
> [mailto:maxima-bounces at math.utexas.edu] On Behalf Of Shahir Molaei
> Sent: Tuesday, March 18, 2008 9:02 PM
> To: maxima at math.utexas.edu
> Subject: Re: [Maxima] Matrices of indefinite size
>
> The last output line of the following code -which I took from
> your article and just replaced the 'mysum' function with
> 'sum' in- returns 'false' :
>
> am:lambda([i,j],a[i,j])\$
> bm:lambda([i,j],b[i,j])\$
> unitm:lambda([i,j],k_delta(i,j));
> matmul(R,S):=
> block([rrow:part(R,1,1),
> scol:part(S,1,2),
> index:?gensym()],
> apply(lambda,[[rrow,scol],
> sum(R(rrow,index)*S(index,scol),index,1,n)]));
> is((matmul(am,unitm)-am)=0);
>
> > -----Original Message-----
> > From: fateman at cs.berkeley.edu
> > Sent: Tue, 18 Mar 2008 14:42:05 -0700
> > To: shahir at inbox.com
> > Subject: RE: [Maxima] Matrices of indefinite size
> >
> > I looked through that article. What did you try that did not work in
> > Maxima?
> > RJF
>
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```