BGradient.m

function [derivee] = BGradient(sigma, a, b, x, y)
    derivee = 0;
    N = size(x,1);
    for i=1:N
        derivee = derivee + ((a*x(i)+b-y(i))/(sigma^2 + ((a*x(i)+b-y(i))^2)));
    end
end