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MathGroup Archive 2000

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Speeding up Inverting matrices.

  • To: mathgroup at smc.vnet.net
  • Subject: [mg23010] Speeding up Inverting matrices.
  • From: David McGloin <dm11 at st-andrews.ac.uk>
  • Date: Tue, 11 Apr 2000 23:18:28 -0400 (EDT)
  • Organization: University Of St Andrews
  • Sender: owner-wri-mathgroup at wolfram.com

I wish to solve the matrix equation Ax = b for x where A is a 24 x 24
matrix and x and b are column matrices. Most of the values in the matrix
are numbers (and many are equal to zero), but one remains unevaluated
i.e element [1,10] may be 160 + d, where d is unevaluated. Currently
we're using the command:

x = {Inverse [A]. b}

this works fine for the smaller matrices we use (8 x 8 and 16 x 16) but
the calculation has now be runing for over 2 days (the smaller matrices
may take many minutes if not seconds). The program is running on a PII
350MHz with 64Mb of RAM. Does anyone have any ideas about how to
optimise our calculation?

Ultimately I want to extract arbitary elements of x and plot them
against the unevaluated element.

Thanks for any help!

David

--
***************************************
David McGloin
Dept. of Physics
Univ. of St. Andrews
dm11 at st-and.ac.uk




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