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

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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!

Answers (1)

Azzi Abdelmalek
Azzi Abdelmalek on 22 Apr 2016
Edited: Azzi Abdelmalek on 22 Apr 2016
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

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