function m = DHm(a, alpha, d, theta)
m = [cos(theta) -sin(theta)*cos(alpha) sin(theta)*sin(alpha) a*cos(theta);
     sin(theta) cos(theta)*cos(alpha) -cos(theta)*sin(alpha) a*sin(theta);
     0 sin(alpha) cos(alpha) d;
     0 0 0 1];
end
