Solving a coupled ODE in Matlab using matrices

Hi,

I have a system of coupled differential equations that I am trying to solve in matlab. The number of equations can range between 6 and 600, so I decided to use matrices.

Essentially, what I am trying to solve is:

dx/dt+Ax=B

Where: - X is a 600x1 vector - A is a 600x600 matrix, and - B is a 600x1 vector

I have written a matlab program to input the matrices A and B, and then attempted to use ode23 to solve f=B-A*x, however it is telling me it will take millions of years to solve.

Please let me know if you require any more information.

Any help is greatly appreciated.

Cheers, Peter