how to find grdient orientation histogram?

i found the gradient and magnitude with this code but i dont know how to find gradient orientation histogram.if u know help me

    angle = 360;

    [GradientX,GradientY] = gradient(double(img));
    Gr = sqrt((GradientX.*GradientX)+(GradientY.*GradientY)); 
    index = GradientX == 0;
    GradientX(index) = 1e-5;     YX = GradientY./GradientX;     
    A = ((atan2(GradientY,GradientX)+pi)*180)/pi;