Failure in initial objective function evaluation. FSOLVE cannot continue

Hello, I'm trying to solve a non-linear system with fsolve and getting this error: " Failure in initial objective function evaluation. FSOLVE cannot continue". I tried looking for previously posts about this issue but without success. The main code is:

options = optimset('MaxFunEvals',1000,'TolFun',1e-8,'Display','off');

    x0 = [300 1];
    x = fsolve(@(x)lista1b_fct(x),x0,options)

and the function is:

parametros

function res = lista1b_fct(x)

Tee = x(1);
Cee = x(2);

res(1) = q*Cf - q*Cee - V*k0*Cee*exp(-E/(R*Tee));
res(2) = q*cp*(Tf - Tee) + deltaH*V*k0*Cee*exp(-E/(R*Tee)) - hA*(Tee - Tc);
end

[Declan Oberbreckling-Schmitt]

Try putting 'res' in brackets so that it's like:

function [res] = listsa1b_fct(x)

If that doesn't work, trying using a different variable name than res. It worked for me. I have no idea why.

Answer 1

[Basil C.]

I guess the mistake you are making is in using

 Tee = x(1);
Cee = x(2);

Rather it should be

 Tee = x0(1);
Cee = x0(2);

Answer 2

[Alan Weiss]

I think that you are missing parameters:

function res = lista1b_fct(x)
Tee = x(1);
Cee = x(2);
res(1) = q*Cf - q*Cee - V*k0*Cee*exp(-E/(R*Tee));
res(2) = q*cp*(Tf - Tee) + deltaH*V*k0*Cee*exp(-E/(R*Tee)) - hA*(Tee - Tc);
end

What is q? What is Cf? What is Cee? Etc. You have a lot of parameters that you need to pass to the function. For documentation on this subject, see Passing Extra Parameters.

One way to do so is to use a structure such as the following in your workspace before you call your function:

params.q = q; % I assume that you have a variable q in your workspace
params.Cf = Cf; % etc.

Then rewrite your function as follows:

function res = lista1b_fct(x,params)
q = params.q;
Cf = params.Cf; % etc
% And so on. Then:
Tee = x(1);
Cee = x(2);
res(1) = q*Cf - q*Cee - V*k0*Cee*exp(-E/(R*Tee));
res(2) = q*cp*(Tf - Tee) + deltaH*V*k0*Cee*exp(-E/(R*Tee)) - hA*(Tee - Tc);
end

Your workspace should call fsolve like this:

[x,fval,exitflag,output] = fsolve(@(x)lista1b_fct(x,params),x0,options)

Alan Weiss

MATLAB mathematical toolbox documentation