[Matlab] Algorytm całkowania metodą prostokątów

%ProstMethod('x^2 +4',1,6,1)
%ans =    75

function [ w ] = ProstMethod( f, a, b, d)
s = 0;
syms x;
f = eval(f);
x = [a:d:b];
    for i = 1:(length(x) - 1)
        s = s + subs(f,x(i))*d;
    end
w = s;
end