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MathGroup Archive 2001

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Re: SetDelayed problems with matrix operation

  • To: mathgroup at smc.vnet.net
  • Subject: [mg27359] Re: SetDelayed problems with matrix operation
  • From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
  • Date: Thu, 22 Feb 2001 02:25:05 -0500 (EST)
  • Organization: Universitaet Leipzig
  • References: <96vv3k$ks@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Hi,

but the right hand side is not evaluated and the symbolic
expression MatrixExp[A t].{b1,0,0} is a singel expression and
not a list of three expressions.

If you have a fixed value for t you can comput the vector on the
right hand side. 

You definition should be

x[i_Integer][t_?NumericQ]:=Part[MatrixExp[A t].{b1, 0, 0},i]

Regards
  Jens

"SANCHEZ DE LEON, Guillermo" wrote:
> 
> Given a square matrix such as
> 
> A={{-3, 0, 0.05}, {0.8, -0.01, 0}, {0, 0.01, -0.05}}
> 
> I wish evalute the expresion:
> 
> { x1[t_], x2[t_], x3[t_]} : = MatrixExp[A t].{b1, 0, 0}
> 
> I receive the message
> 
> SetDelayed::"shape": "Lists{ x1[t_], x2[t_], x3[t_] } and  MatrixExp[A t)] .
> {b1, 0, 0} are not the same shape."
> 
> But it is known that when MatrixExp[A t].{b1, 0, 0} will be evaluate , given
> a  value for t,  the solution  will be already a list of the same shape that
> Lists{ x1[t_], x2[t_], x3[t_]}
> 
> For instance:
> 
> MatrixExp[A t].{b1, 0, 0}/.t->3 it work fine.
> 
> How it will be build the the expresion { x1[t_], x2[t_], x3[t_]} : =
> MatrixExp[A t].{b1, 0, 0} to be evaluated?


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