function [p, next_delay] = pulse_train(period ,len, init_delay)
%
% [p, next_delay] = pulse_train(period,len, init_delay) 
%	generates an impulse train:
%
%	period = period of the impulses in the impulse train (an integer).
%	len = length of impulse train in samples
%	init_delay = delay  of the first pulse (default 0)
%	p = output pulse train
%	next_delay = delay to first pulse in next frame
%
%
if nargin < 3, init_delay = 0; end
 
% Initialize impulse train.
p = zeros(1,len);

% Place impulses
pulse_times = init_delay+1:period:len;
if ~isempty(pulse_times),
   p(pulse_times) = ones(size(pulse_times));

   % find time to next pulse
   next_delay=max(pulse_times)+period-len-1;

else
   next_delay = init_delay - len;
end