function y = decay(t,etc);
%function y = decay(t,etc);
%
%   Decay function exp(-t/t0)*cos(omega*t)
%   t = list of times
%   etc contains t0, omega
%   t0 = time constant
%   omega = radian frequency
%
error(nargchk(2,2,nargin));
t0 = etc(1);
omega = etc(2);
y = exp(-t/t0).*cos(omega*t);