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?