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MathGroup Archive 1998

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Numerical Determinants

  • To: mathgroup at smc.vnet.net
  • Subject: [mg12922] Numerical Determinants
  • From: hello at there.com (Rod Pinna)
  • Date: Wed, 24 Jun 1998 03:44:42 -0400
  • Organization: UWA
  • Sender: owner-wri-mathgroup at wolfram.com

Hello all,

I have a large square matrix, of 30x30 elements (and possibly  larger).
Each element is of the form

        Ai,j + Bi,j P

Where Ai,j and Bi,j are real numbers. Evaluation of this matrix  in
symbolic form is very slow. Obviously, numeric evaluation is  much
faster. What I want to do is evaluate, with M the matrix  above:

NSolve[Det[M]==0,P]

Nsolve seems to, as far as I can tell, first evaluate a symbolic 
expansion of M, rather than numerically substituting numbers. Is  there
a way to get Mathematica to evaluate this in a purely numeric way?

I've tried Findroot, but the fuction is badly behaved around the  roots
of interest, and it doesn't find the roots I'm looking for. Any
suggestions?

Thanks,
Rod Pinna.


Rod Pinna
(rpinnaX at XcivilX.uwa.edu.au  Remove the X for email)



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