fsolve usage in Simulink fails due to P-code error

Hi,

I would to solve an expression numerically using fsolve in Simulink however I get a P-code function error which I cannot understand.

I am trying to solve the following function in a matlab function block in simulink which works when used in a Matlab script:

function [lam_the] = slip_mag(theta)
    % Magic formula
    % Unpack
    B0 = theta(1,1);
    C0 = theta(1,2);
    D0 = theta(1,3);
    E0 = theta(1,4);
    mu0 = theta(1,5);
    
    % Solve
    F = @(sig) (D0 * sin(C0 * atan(B0 * sig - E0 * (B0 * sig - atan(B0 * sig)))) - mu0);
    opt = optimoptions('fsolve','Algorithm',"levenberg-marquardt");
    lam_the = fsolve(F,0.1,opt);
end

Which results in the following error:

Simulink does not have enough information to determine output sizes for this block. If you think the errors below are inaccurate, try specifying types for the block inputs and/or sizes for the block outputs.
Component: MATLAB Function | Category: Coder error
Index expression out of bounds. Attempted to access element 1. The valid range is 1-0.
More information

P-code function 'driver.p' produced an error.
Component: MATLAB Function | Category: Coder error
Function call failed.

P-code function 'fsolve.p' produced an error.
Component: MATLAB Function | Category: Coder error
Function call failed.

Function 'Particle Filter1' (#24.3081.3098), line 95, column 15:
"fsolve(F,0.1,opt)"
Launch diagnostic report.
Component: MATLAB Function | Category: Coder error

How can I correctly use fsolve in Simulink?

Thank you in advance.

Answer 1

[Christian]

Initialize lam_the=0; in the first line of the function.

Matlab just fails to provide a proper Error.