function v = funcao_mae_mexicana(z,sigma)
zc = z;
zg = z/sigma;
if abs(zg) < 8.5
    if abs(zc) < 1.0e-6
        vc = 1;
    else
        vc = sin(pi*zc)/(pi*zc);
    end
    v = vc*exp(-.5*zg^2);
else
    v = 0;
end