matlab code to find the difference in the Histogram of Oriented Gradients(HOG) of two images

how to compute HOG using a single LxL rectangular cell with 9 histogram bins(20 degree per bin) and L2 normalization. thus HOGs for both 9 element vectors, where each entry denotes the relative amount of the respective 9 orientations +/- 20, 60, 100, 140 and 180 deg. compute the dissimilarity between 2 HOGs