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MathGroup Archive 2005

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Re: Wierd problems with Mathematica - inversion of a 12x12 matrix

  • To: mathgroup at smc.vnet.net
  • Subject: [mg56110] Re: Wierd problems with Mathematica - inversion of a 12x12 matrix
  • From: Andreas Stahel <sha at hta-bi.bfh.ch>
  • Date: Fri, 15 Apr 2005 04:48:35 -0400 (EDT)
  • References: <d3lrsq$sef$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Madhusudan Singh <spammers-go-here at spam.invalid> writes:
Hello

you might want to try not to display the result. Use a ";" to
terminate the command. Then access only one compoment of your matrix
at a time. I had Mathematica freeze up on me on serveral occasion
during the fomatting for display on screen.

Hope this helps

Andreas

> 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.
> 
> 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 with FullSimplify) that it is impossible to
> make sense of.
> 
> OTOH, the graphical Notebook is still chugging away. Has anyone seen this
> odd behaviour before ?
> 
> Thanks.
> 

-- 
Andreas Stahel       E-Mail: Andreas.Stahel at [ANTI-SPAM]hti.bfh.ch
Mathematics, HTI     Phone: ++41 +32 32 16 258
Quellgasse 21        Fax:   ++41 +32 321 500
CH-2501 Biel         WWW:   www.hta-bi.bfh.ch/~sha
Switzerland


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