myxcorr2(a,b)

function c = myxcorr2(a,b)
%MYXCORR2 Two-dimensional FFT accelerated periodic cross-correlation of 
%   the matrices A and B representing periodic functions.
%   MYXCORR2(A,B) computes the periodic crosscorrelation of matrices A and
%   B.
%   MYXCORR2(A) is the periodic autocorrelation function.
%
%   See also CONV, CONV2, XCORR, MYCONV, MYCONV2, MYXCORR
%
%   clear all;
% 
%   % Create a "measurement" domain
%   Lx = 1e-3;            Ly = 1e-3;
%   Nx = 2^7;             Ny = 2^7;
%   x  = Lx*(0:Nx-1)/Nx;  y  = Ly*(0:Ny-1)/Ny;
%   dx = x(2)-x(1);       dy = y(2)-y(1);
%   [X,Y] = meshgrid(x,y);
% 
%   % "Sample" the (periodic) signal
%   z  = cos(2*pi*2*X/Lx).*cos(2*pi*1*Y/Ly)+...
%     0.5*cos(2*pi*5*(X-0.14*Lx)/Lx).*cos(2*pi*7*(Y-0.02)/Ly)+...
%     0.25*cos(2*pi*16*(X-0.3*Lx)/Lx).*cos(2*pi*10*(Y+0.32)/Ly)+...
%     0.25*cos(2*pi*18*(X-0.7*Lx)/Lx).*cos(2*pi*22*(Y-0.02)/Ly);
% 
%   % z  = [zo(:,end-Nx/2+1:end),zo,zo(:,1:Nx/2)]; % Periodic ext. removing edge-effects
%   % z  = [z(end-Ny/2+1:end,:);z;z(1:Ny/2,:)];
%   [Nzy,Nzx] = size(z);
% 
%   % Filter weighting function
%   lcx = Lx/2;  % Cut-off acc to ISO 11562 Gaussian Profile Filter Lx/5
%   lcy = Ly/2;
%   Xf  = [X,X(:,end)+dx]-Lx/2; % Symmetric and ensure that Nx+Nh-1 = 2^k
%   Xf  = [Xf;Xf(1,:)];
% 
%   Yf = [Y;Y(end,:)+dy]-Ly/2;
%   Yf = [Yf,Yf(:,1)];
% 
%   variancex = 1/(pi*sqrt(2/log(2)))*lcx;
%   variancey = 1/(pi*sqrt(2/log(2)))*lcy;
%   hx = dx/(sqrt(2*pi)*variancex)*...
%     exp(-((Xf/variancex).^2)/2);
%   hy = dy/(sqrt(2*pi)*variancey)*...
%     exp(-((Yf/variancey).^2)/2);
%   [Nhy,Nhx]  = size(hx); %=size(hy)
% 
%   % Total length of the padded arrays needed for the fft operations
%   N = Nzx+Nhx-1;
%   M = Nzy+Nhy-1;
% 
%   % Cross correlation - built in function
%   tic;
%   xc = xcorr2(z,z);
%   toc;
% 
%   % Cross correlation - A. Almqvists fft accelerated version
%   tic;
%   xf = myxcorr2(z,z);
%   toc;
% 
%   % Plotting the results
%   plot(...
%     1:N-1, xc(1,:)    , 'k.' ,...Filtered - spatial domain
%     1:N-1, xf(1,:)    , 'r--'...Filtered - freq. domain
%     );

%   Author(s): A. Almqvist
%   Copyright 2009- Andreas Almqvist
%   $Revision: 1$  $Date: 2009/11$
%   Homemade function

if nargin == 1
	b = a;
end
c = myconv2(a,rot90(conj(b),2));