Error: Not enough input arguments.

The following code works fine.

See the inline function fungrad.

 function [x, fval, eflag, iter, fcount] = 
          Optimization_With_Analytic_Gradient(start_point)

    x0 = start_point;

    %   inline function defitions
    fungrad = @(x)deal(fun(x),grad(x));

    % options setup
    options = optimoptions( 'fminunc', ...
                            'Display','off',...
                            'OutputFcn',@bananaout,...
                            'Algorithm','trust-region', ...
                            'GradObj','on');

    % calling fminunc
    [x,fval,eflag,output] = fminunc(fungrad,x0,options);
    iter = output.iterations;
    fcount = output.funcCount;

    %   plot window title
    title 'Rosenbrock solution via fminunc with gradient'    

    disp('Optimization_With_Analytic_Gradient...');
end

But, when I call it using the following code,

 function out = fungrad(x)
     out = deal(fun(x),grad(x));
 end

It displays the following error:

 Error using fungrad (line 2)
 Not enough input arguments.

 Error in Optimization_With_Analytic_Gradient (line 24)
    [x,fval,eflag,output] = fminunc(fungrad,x0,options);

 Error in main (line 48)
        [x, fval, eflag, iter, fcount] = 
    Optimization_With_Analytic_Gradient(starting_point);

Rest of the code:

 function out = fun(x)
     out = 100*(x(2) - x(1)^2)^2 + (1 - x(1))^2;
 end

 function out = grad( x )
     out = [-400*(x(2) - x(1)^2)*x(1) - 2*(1 - x(1)); 
            200*(x(2) - x(1)^2)];
 end

Answer 1

[Walter Roberson]

      [x,fval,eflag,output] = fminunc(@fungrad,x0,options);

However, your code will not work. Your objective function must return the gradient information only when nargout > 1. Your use of deal() always returns two outputs, and that is going to fail.

Refer to http://www.mathworks.com/matlabcentral/answers/318706-problem-running-fmincon-input-arguments-to-function-include-colon-operator#comment_417378

[Ba Ba Black Sheep!]

 Your objective function must return the gradient information 
 only when nargout > 1.

which one? banana? or, fungrad?

_

N.B. Sorry! I am absolutely new.

[Walter Roberson]

You have

      fungrad = @(x)deal(fun(x),grad(x));

so your fungrad is always returning two outputs. fungrad is being used as your objective function for fminunc . The objective function must only assign the gradient when it is asked to do so. See the example https://www.mathworks.com/help/optim/ug/fminunc.html#butzm_r-1 and notice that it tests nargout