readme file for matlab_scripts.zip 

% Yuan Qi
% yuanqi@media.mit.edu
% MIT Media lab, Affective computing group
% June 10 2002

This zip file includes

kalman_defaults.mat
kalmspectr_irspl.m
spectroentrpy.m
usekalmspectr.m
entropy.m
entropysmpl.m
histogram.m

Among all the unziped files, spectroentrpy.m is the main file, which computes the entropy of the spectrogram of a given signal x.

function [entest, mapl]= spectroentrpy(x, t, NN, fsig, fdisp)
% x: signal
% t: sampling time
% NN: number of frequency bands
% fsig: spectrom range [0 ~ fsig/2] . Default: 1.2
% fdisp: graphic output or not. Default: 1
% entest: the entropy value of the spectrogram
% mapl: the spectrogram
 
For example, x is the heart rate signal and
t is the sampling time, which can be evenly or unevenly 
spaced. If we want the frequency resolution of the 
spectrum to be 100, spectrom range to be 0 to 1.0 Hz, and have graphic output, then NN = 100, fsig = 2.0, and fdisp = 1.

Running "[entest, mapl]= spectroentrpy(x, t, NN, fsig, fdisp)" 
in matlab enviroment, we  obtain  the entropy value of the spectrogram of the heart rate, which measures the heart rate variability. The spectrogram of the heart rate is saved in the output "mapl" correspondingly.