If you just want to run it from Simulink, just call your function as extrinsic. For example if your function is called myfun(a,b,c), and if myfun(a,b,c) returns, say, a 3-by-1 int32 vector, then your MATLAB function block would look something like
function y = fcn(a,b,c)
y = zeros(3,1,'int32');
y = myfun(a,b,c);
Just put your function in the same directory as the model or somewhere on the path.