Error in 'Project_c​omplete_tr​y/Vehicle Dynamics/Longitudinal State Space Matrix' while executing MATLAB S-function 'ss_lon_sfcn', flag = 1 (derivatives), at time 0.0.

function [sys,x0,str,ts]=ss_lon_sfcn(t,x,u,flag,xinit)

switch flag

 case 0 % initialize

 str=[] ;

 ts = [0 0] ;

 s = simsizes ;

 s.NumContStates = 4 ;

 s.NumDiscStates = 0 ;

 s.NumOutputs = 4 ;

 s.NumInputs = 1 ;

 s.DirFeedthrough = 0 ;

 s.NumSampleTimes = 1 ;

 sys = simsizes(s) ;

 x0 = xinit ;

 case 1 % derivatives

 sys = ss_lon(t,x,u) ;

 case 3 % output

 sys = x;

 case {2 4 9}

 % 2:discrete

 % 4:calcTimeHit

 % 9:termination

 sys =[];

 otherwise

 error(['unhandled flag =',num2str(flag)]) ;

end

where the function is as:

function lon_dynamics = ss_lon(t,x,u)

if t>=0 && t<1

A_MATRIX = evalin('base', 'A_MATRIX:,:,1)');

B_MATRIX = evalin('base', 'B_MATRIX:,:,1)');

elseif t>=1 && t<2

A_MATRIX = evalin('base', 'A_MATRIX:,:,1)');

B_MATRIX = evalin('base', 'B_MATRIX:,:,1)');

elseif t>=2 && t<3

A_MATRIX = evalin('base', 'A_MATRIX:,:,2)');

B_MATRIX = evalin('base', 'B_MATRIX:,:,2)');

elseif t>=3 && t<4

A_MATRIX = evalin('base', 'A_MATRIX:,:,3)');

B_MATRIX = evalin('base', 'B_MATRIX:,:,3)');

end

lon_dynamics = A_MATRIX*x+B_MATRIX*u;

end