function [OA,OV] = overlap(X,GZ,NCC,NCA,dA)
% This routine takes as its central argument the matrix
% GZ. This has one column for each animal whose home range
% was computed by some other method and one row for each
% point in the x,y sample grid. The values in GZ for any 
% column are the probabilities that the animal represented
% by that column would be found at that grid point.  The
% matrix X has as many columns as the number of animals being
% compared. Each column is filled with 0's except for the row
% corresponding to the column in GZ that is to be included:
% this cell has a 1 in it. The matrix NCC
% contains one more column than the number of 
% animals considered. The first column contains the % of the
% total home range volume sought. The subsequent values in the
% same row give the minimal probability for the animal in that
% column that contribute to the % cutoff in the first column of
% NCC. The matrix NCA has the same first column, but gives the
% area at each cutoff for each animal.The value dA is the area/cell 
% of the grid. The results are two matrices. The first column of each
% reproduces the first column in NCC. The second column of OA gives the
% area of overlap for the given contrast at the given cutoff. The
% subsequent columns give the % of that cutoff area represented by the
% overlap area for each animal. The output matrix OV has as first
% column the cutoff %. The subsequent columns give the total probability 
% of finding each animal in that overlap zone.
% Jack Bradbury, Cornell University, December 2000.
GZZ=GZ*X;              % reduce GZ matrix to those columns being compared
[n,m]=size(GZZ);       % Get new size of reduced matrix
[r,p]=size(NCC); 
NC=NCC(:,2:p)*X;    % Reduce NCA and NCC matrices accordingly
NA=NCA(:,2:p)*X;
OA=[];
OV=[];
[g,h]=size(NC);
for i=1:g
	DC=repmat(NC(i,:),n,1);
	DD=GZZ-DC;
	for j=1:m
		if (~isempty(DD))
			[MM,id]=find(DD(:,j)>=0);
			DD=DD(MM,:);
		end
	end
	if (~isempty(DD))
		[k,l]=size(DD);
		DC=repmat(NC(i,:),k,1);
		DD=DD+DC;
		SA=k*dA;                  % Compute area of overlap zone
		OA=[OA;SA 100*(SA)./NA(i,:)];       % Store fraction of each animal area in overlap
		VA=100*sum(DD,1);           % Get % volume of each animal in overlap
		OV=[OV;VA];
	else
		w=zeros(1,(m+1));
		OA=[OA;w];
		v=zeros(1,m);
		OV=[OV;v];
	end
end
OV=[NCC(:,1) OV];
OA=[NCC(:,1) OA];