Re: Symbolic inverse of a 12x12 matrix (Interesting developments)

Madhusudan Singh wrote:

> Hi
>
> I am solving a problem using f95 that involves solving a 12x12 coupled
> linear system. I have written out the matrix A (A x = f), and instead of
> calculating the inverse repeatedly for different values of the input
> parameters, I am trying to calculate the symbolic inverse of the matrix,
> post multiply it with the RHS and code the resulting 12 equations for x_i
> into fortran.
>
> I believe this is the sensible way to do it, since this system needs to be
> solved lots of times (its part of a half-infinite integral) and inverting
> such a system numerically would not only be time consuming, but also
> obscure possible stability problems.
>
> Now, I am using Mathematica 5.1 (multiprocessor Sun machine) to do it, but
> the inverse has been running for the past 40 minutes without any result. A
> prior attempt to run it with Mathematica 4.1 (single processor Pentium M
> Linux machine) resulted in an aborted process.
>
> I am wondering if such long inversion times for this medium sized system
> are typical for Mathematica. Could I make it faster by compiling the
> notebook in some fashion ? I have sparingly used maxima (formerly known as
> macsyma) in the past, and have heard that it generally gives faster
> results than Mathematica does. Is it reliable enough to make it worthwhile
> to try that ? Mathematica makes it possible to render the result in a
> human readable format using MatrixForm. Is such a device available in
> maxima (if it is suitable for this task) ?
>
> Though I have not heard good things about Matlab's symbolic computation
> package, is that also a tool worth trying ?
>
> Thanks.

Hi

Out of a hunch, I just exported the notebook to text, and used "math" (the
text version of Mathematica) to run it through. Less that two minutes
later, I had an answer. The problem is that the answer (in nohup.out) is so
ill formatted (I used MatrixForm) that it is impossible to make sense of.

OTOH, the graphical Notebook is still chugging away. Has anyone seen this
odd behaviour before ?

Thanks.
.

Relevant Pages

  • Re: Symbolic inverse of a 12x12 matrix
    ... > I am solving a problem using f95 that involves solving a 12x12 coupled ... > linear system. ... > prior attempt to run it with Mathematica 4.1 (single processor Pentium M ... I have sparingly used maxima ...
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  • Re: Symbolic inverse of a 12x12 matrix
    ... >> I am solving a problem using f95 that involves solving a 12x12 coupled ... As bourne out by your execution times. ... The long execution time seems to be related to the time Mathematica spends ... on rendering the result as Marcus pointed out. ...
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