% RES = CCONV2(MTX1,MTX2)
%
% Circular convolution of two matrices.  Result will be of size of
% LARGER vector.
%
% EPS, 6/96.

function c = cconv(a,b)

if (( size(a,1) >= size(b,1) ) & ( size(a,2) >= size(b,2) ))
    large = a; small = b;
elseif  (( size(a,1) <= size(b,1) ) & ( size(a,2) <= size(b,2) ))
    large = b; small = a;
else
  error('one arg must be larger than the other in both dimensions!');
end

ly = size(large,1);
lx = size(large,2);
sy = size(small,1);
sx = size(small,2);
sy2 = floor(sy/2);
sx2 = floor(sx/2);

% pad:
clarge = [ 
    large(ly-sy2+1:ly,lx-sx2+1:lx), large(ly-sy2+1:ly,:), ...
	large(ly-sy2+1:ly,1:sx-sx2-1); ...
    large(:,lx-sx2+1:lx), large, large(:,1:sx-sx2-1); ...
    large(1:sy-sy2-1,lx-sx2+1:lx), ...
	large(1:sy-sy2-1,:), ...
	large(1:sy-sy2-1,1:sx-sx2-1) ];

c = conv2(clarge,small,'valid');