Failure in initial objective function evaluation. FMINUNC cannot continue.

I tried to evaluate this function but I am getting this error Failure in initial objective function evaluation.

FMINUNC cannot continue.

Please what is the best way to evaluate this function

f = x(2)^2*x(9)^2 + x(2)^2*x(9) + x(2)^3*x(9) - x(3)*x(5)*x(9)^2 + x(6)*x(8)*x(9)^2 + x(6)*x(8)*x(9)^3 + x(2)*x(6)*x(8)*x(9)^2;

Answer 1

[Star Strider]

Unless it is already in a function file, it needs to be an anonymous function:

f = @(x) x(2)^2*x(9)^2 + x(2)^2*x(9) + x(2)^3*x(9) - x(3)*x(5)*x(9)^2 + x(6)*x(8)*x(9)^2 + x(6)*x(8)*x(9)^3 + x(2)*x(6)*x(8)*x(9)^2;

If it is in a function file (and you have passed the function handle to fminunc correctly), the initial parameter estimates could be the problem. Please post those.

[Kelechi Emerole]

These are the code, am I doing anyhthing wrong? Sorry I am new to matlab


fun =@(x)x(2)^2*x(9)^2 + x(2)^2*x(9) + x(2)^3*x(9) - x(3)*x(5)*x(9)^2 + x(6)*x(8)*x(9)^2 + x(6)*x(8)*x(9)^3 + x(2)*x(6)*x(8)*x(9)^2;
x0 = [-.5, 0];
options = optimoptions('fminunc','Algorithm','quasi-newton');
options.Display = 'iter';
[x, fval, exitflag, output] = fminunc(fun,x0,options);

[Star Strider]

You have 9 parameters, so ‘x0’ must have 9 elements.

For example —

fun =@(x)x(2)^2*x(9)^2 + x(2)^2*x(9) + x(2)^3*x(9) - x(3)*x(5)*x(9)^2 + x(6)*x(8)*x(9)^2 + x(6)*x(8)*x(9)^3 + x(2)*x(6)*x(8)*x(9)^2;
x0 = rand(9,1);
options = optimoptions('fminunc','Algorithm','quasi-newton');
options.Display = 'iter';
[x, fval, exitflag, output] = fminunc(fun,x0,options);

This runs without error, however I doubt the result is what you want.

[Kelechi Emerole]

Thanks very much Sir, it runs but ends up with this problem. How do I solve it? Thanks once agian.

fminunc stopped because the objective function value is less than
or equal to the default value of the objective function limit.

[Star Strider]

That is not an error or a problem. It is simply a message from fminunc that it stopped, and the reason.

Meanwhile, consider changing your fminunc call to:

[x, fval, exitflag, output] = fminunc(@(x)norm(fun(x)), x0, options);

That may be the result you want.

[Kelechi Emerole]

Wow thank you Sir for your quick reply, it produced this line, is that a problem?

fminunc stopped because it cannot decrease the objective function
along the current search direction.

[Kelechi Emerole]

Mr Star strider, thank you very much. I have gotten the result I want.

[Star Strider]

As always, my pleasure!

It is not a probllem. Again, fminunc is simply telling you that it stopped, and the reason.

[Mohammed Ouallal]

It seems that you resolve the problem but did not show how! please be kind and share the complete solution.

Thank you for the understanding!

[Star Strider]

Yes, I did!

‘Unless it is already in a function file, it needs to be an anonymous function’