Fast mutual information of two images or signals

Usage: I=mi(A,B), where A and B are equally sized images/signals.
Function hist2 (included) is used to determine the joint histogram of the images/signals.

Assumptions: 1) 0*log(0)=0, 2) mutual information is obtained on the intersection between the supports of partial histograms.

Example (in mi_test.m):

disp('Test: Mutual information between two images')
load mri
A=D(:,:,8);
B=D(:,:,9);
mi(A,B)

disp('Test: Mutual information between two signals')
load garchdata
nasdaq = price2ret(NASDAQ);
nyse = price2ret(NYSE);
mi(nasdaq,nyse)