Matrix differential equation in NDSolve

*To*: mathgroup at smc.vnet.net*Subject*: [mg63298] Matrix differential equation in NDSolve*From*: Maarten <maarten at stack.nl>*Date*: Fri, 23 Dec 2005 05:08:24 -0500 (EST)*Sender*: owner-wri-mathgroup at wolfram.com

Hello, I would like to evaluate a matrix equation of the form: S'[t]==A(x).S[t]+B(x) x'[t]==f[x] in NDSolve where A and B are symbolic matrices. The problem is that S[t] is an unknown n x m matrix, of the same dimension as B. If I enter the first equation as shown above, Mathematica evaluates it to {A(x).S[t]+B(x){1,:},A(x).S[t]+B(x){2,:},...,A(x).S[t]+B(x){m,:}} that is, it assumes S[t] is a vector which is replicated to match the dimensions of B(x). How can I get Mathematica to respect the fact that S[t] is of dimension B in NDSolve. I tried holdform but this does not evaluate in NDSolve