Why in Simulink a Matlab function block changes its output when changing the solver?

Hello,

I have in Simulink a Matlab function block with some equations written inside.

The problem comes when I change the solver from ODE1 (Euler) to ODE4 (Runge-Kutta), always using fixed step time.

How come that I get different output values if the outputs are direct equations of the inputs? Should not be they the same independently of the solver I chose?

Here the code:

 function x = fcn(T, A, B, u)

 persistent x_1 u_1
 if isempty(x_1)
    x_1 = 0;
    u_1 = 0;
 end

 x = x_1 + T * (A * x_1 + B * u_1);

 x_1 = x;
 u_1 = u;

Thanks!

Answer 1

[Azzi Abdelmalek]

It happens that Simulink gives different results for different solvers, especially when the type of equations it has to solve, requires an appropriate solver. Read how to choose a solver. http://www.mathworks.com/help/simulink/ug/types-of-solvers.html