function [To]=xyexpand(Tin,niter)
% Tout=xyexpand(Tin,3);
% 
% This function takes 2D input and replaces any NaN
% neighbouring any real numbers with the average of
% those numbers. This procedure is repeated niter
% times. Note that the ocean/land volume ratio expands
% rapidly with each iteration.
%
% In short, this is a gap-filler and extrapolator of
% rudimentary order applied to horizontal slices.
%
% Created  08/15/99 by adcroft@mit.edu
% Modified 11/11/99 by adcroft@mit.edu
% Maintained by adcroft@mit.edu, abiastoch@ucsd.edu

[nx,ny]=size(Tin);
ip=[2:nx 1];
im=[nx 1:nx-1];
jp=[2:ny ny];
jm=[1 1:ny-1];

T=Tin;
for iter=1:niter,

msk=ones(nx,ny);
L=isnan(T);
msk( L )=0;

To=T;
To( L )=0;

cnt=msk(im,:)+msk(ip,:)+msk(:,jm)+msk(:,jp);
cnt( find(cnt==0) )=1;
Tbr=(To(im,:)+To(ip,:)+To(:,jm)+To(:,jp))./cnt;

To( L )=Tbr( L );

To( find(To==0) )=NaN;

T=To;
end