Error: Undefined function <func_name> for input arguments of type 'double'.

Below is a small part of the big code, Where I'm getting an error at line 3. Undefined function 'f1' for input arguments of type 'double'.

Below I've changed the code little bit as compared to the source to make it more readable.

function fit = dummy(x)
fhd = str2func('f1');
fit = feval(fhd, x); % Error Here

%------------------------------------------------------------------------------
% Elliptic Function
%------------------------------------------------------------------------------
function fit = elliptic(x)
    %TODO Do we need symmetry breaking?
    %TODO Implement to support a matrix as input.

      [D ps] = size(x);
      condition = 1e+6;
      coefficients = condition .^ linspace(0, 1, D); 
      fit = coefficients * T_irreg(x).^2; 
  end

function fit = f1(x)
    persistent xopt lb ub
    [D ps] = size(x);
    load 'datafiles/f01.mat';

      idx = checkBounds(x, lb, ub);
      x = x-repmat(xopt, 1, ps);
      fit = elliptic(x);
      fit(idx) = NaN;
      if ~isempty(idx)
          warning "Some of the solutions are violating boundary constraints.";
      end
  end

end

Please help me to sort out the problem. For the complete code checkout "benchmark_func.m" in the "matlab.zip" attached.

Answer 1

[Guillaume]

I suspect the problem is str2func not seeing the local function. That's the problem with using strings to store code, the JIT compiler doesn't always work properly.

Any reason you're using an outdated method of creating and using function handles?

fhd = @f1;
fit = fhd(x);

would work, is simpler and possibly faster as well.

If f1 is one of many possibilities to be chosen by that dummy function:

fchoices = {@f1, @f2, @f3};
fhd = fchoices{choice};
fit = fhd(x);

[Stephen23]

+1 for recommending function handles (much better than awful strings).

Answer 2

[Massimo Zanetti]

Refer to your 2nd line of code

fhd = str2func('f1');

The string 'f1' evaluates to nothing in Matlab, therefore the command

fit = feval(fhd, x);

fails. To let it work, 'f1' must be an anounimous function definition. Read str2func help page.