As I already answered, f has to be referenced as a function or a function handle in your case.
It cannot be given in the GUI - all inputs in the GUI can only be constant values.
c = 1;
a = 1;
theta1 = 0.1;
theta2 = 0.1;
specifyCoefficients(model,"m",0,"d",0,"c",c,"a",a,"f",@(location,state)fcoeffunction(location,state,theta1,theta2));
function f = fcoeffunction(location,state,theta1,theta2)
N = 1; % Number of equations
nr = length(location.x); % Number of columns
f = zeros(N,nr); % Allocate f
% Now the particular functional form of f
f(1,:) = 100*sin(2*pi*location.x).*sin(2*pi*location.y) - theta1/theta2*exp(theta2*state.u(1,:) - 1);
end
Or as a simple function handle:
c = 1;
a = 1;
theta1 = 0.1;
theta2 = 0.1;
fun = @(location,state,theta1,theta2) 100*sin(2*pi*location.x).*sin(2*pi*location.y) - theta1/theta2*exp(theta2*state.u - 1);
f = @(location,state) fun(location,state,theta1,theta2);
specifyCoefficients(model,"m",0,"d",0,"c",c,"a",a,"f",f);
