function y=H(x,a)
% function Y=H(x,a)
%   Heavyside function returns
%   Y=1      for x > a
%   Y=1/2    for x=a
%   Y=0      for x < a
% 
% this is equivalent to the H(x+a)
% INPUTS: x = the x-axis at which values 
%             need to be returned. 
%         a = constant
% NOTE: H(x-a), you need to y=H(x,-a)
%
% EXAMPLES
%      x=-10:0.2:10; a=3;
%      y=H(x,a);
%      plot(x,y); set(gca,'ylim',[-2 2]);


y=zeros(length(x),1);
in=find(x > -a); if ~isempty(in), y(in)=1;  end;
in=find(x== -a); if ~isempty(in), y(in)=1/2;end;
in=find(x < -a); if ~isempty(in), y(in)=0;  end;