Question

I am trying to find the minimum value of a function of two variables, and then find the value of the variables.

My method is to iterate the function through several values of the variables and then use the min function to find the lowest value.

minval = -10;
maxval = 10;
n = 1;

for x = minval:maxval
    for y = minval:maxval
        f(n) = abs(x-1)+abs(y-1)+abs(x-3)+abs(y-5)+abs(x-8)+abs(y-3);
        n=n+1;
    end
end
f(n) = abs(x-1)+abs(y-1)+abs(x-3)+abs(y-5)+abs(x-8)+abs(y-3);
fmin = min(f)

The problem is with the last line:

fmin = min(f)

I am getting the error

??? Index exceeds matrix dimensions.

Error in ==> Lab2 at 65
fmin = min(f)

Why is this? Any help is greatly appreciated.

Answer 1

It does indeed look like you have declared a variable called min and so Matlab now treats it like a variable and not a function so it thinks you are trying to index the variable min with the vector f.

But just a comment on your code, leaving off whatever f(442) is you could achieve the same thing in a much more matlabesque fashion without loops like this:

minval = -10;
maxval = 10;

X = minval:maxval;
Y = X;

[xx, yy] = meshgrid(X, Y);
F = abs(xx-1) + abs(yy-1) + abs(xx-3) + abs(yy-5) +abs(xx-8) + abs(yy-3);

Your f is now equivalent to F(:)' (without the final value…), prove it to yourself like this: sum(f(1:end-1) == F(:)')

F as a matrix probably makes more sense than f as a flat vector anyway and you can find the min of F like this: min(F(:))