Implementation of grid search for a function

I am trying to run a grid search and find x*. but it gives me "Not enough input arguments".

funktion = @(x) sqrt(x) + 2*sqrt(1-x);

x = [0:0.001:1];

x_star_grid = grid(funktion, x)

function [f_benchmark, domain_max] = grid(funktion, domains)

domain_max = -1e+5;

for i = 1:length(domains)

z= domains(i);

disp(z)

f = feval(funktion, z);

if f>=f_benchmark

f_benchmark = f;

domain_max = domains(i);

end

end

end