function retval = sinenvelope(func, step,len)
% sinenvelope.m
% Created by: Tasha Vanesian
% Use this function to put an sine envelope on the first half of a function.
sine_coefficient = [(sin((pi* [0:step:len/2.0]) / (len)) ) ...
						ones(1, length([len/2.0:step:len]) - 1) ];
retval = func .* sine_coefficient;