mlosch/interp_llc/exch_llc.m

function [b] = exch_llc(a,o)

[nnx nny]=size(a);

if (nnx/4~=round(nnx/4))
  error('x-dimension needs to be divisible by 4')
end
n4 = nnx/4;
% pull array appart
ca  = a(:,end-n4+1:end);
lla = a(:,1:end-n4);
% do the tricky bit first because we need the ll part for that
[nx,ny]=size(ca);
lln = lla(:,end-o+1:end);
cb = NaN*ones(nx+2*o,ny+o);
% interior
cb(o+1:nx+o,1:ny)=ca;
%
cb(1:o,:) = flipud(lln(n4*3-o+1:n4*4,:))'; % right
cb(end-o+1:end,:) = fliplr(lln(1:n4+o,:))'; % left
% top
cb(o+1:o+n4,end-o+1:end) = flipud(fliplr(lln(2*n4+1:3*n4,:)));
cb(o+n4+1:o+2*n4,end-o+1:end) = fliplr(flipud(lln(n4*3+1:n4*4,:)));
cb(o+n4*2+1:o+3*n4,end-o+1:end) = flipud(lln(1:n4,:));
cb(o+n4*3+1:o+4*n4,end-o+1:end) = flipud(lln(2*n4+1:3*n4,:));

% now exchange regular part:
[nx,ny]=size(lla);
llb=NaN*ones(nx+2*o,ny+o);
llb(o+1:o+nx,o+1:o+ny)=lla;                     % Interior
%b(o+1:o+nx,o+ny+(1:o))=a(:,ny:-1:ny-o+1);      % N
%b(o+1:o+nx,1:o)=a(:,o:-1:1);                   % S
llb(o+nx+(1:o),:)=llb(o+1:o+o,:);               % E
llb(1:o,:)=llb(o+nx-o+1:o+nx,:);                % W

% put both parts together

b = [llb cb];


1	function [b] = exch_llc(a,o)
2
3	[nnx nny]=size(a);
4
5	if (nnx/4~=round(nnx/4))
6	error('x-dimension needs to be divisible by 4')
7	end
8	n4 = nnx/4;
9	% pull array appart
10	ca = a(:,end-n4+1:end);
11	lla = a(:,1:end-n4);
12	% do the tricky bit first because we need the ll part for that
13	[nx,ny]=size(ca);
14	lln = lla(:,end-o+1:end);
15	cb = NaNones(nx+2o,ny+o);
16	% interior
17	cb(o+1:nx+o,1:ny)=ca;
18	%
19	cb(1:o,:) = flipud(lln(n43-o+1:n44,:))'; % right
20	cb(end-o+1:end,:) = fliplr(lln(1:n4+o,:))'; % left
21	% top
22	cb(o+1:o+n4,end-o+1:end) = flipud(fliplr(lln(2n4+1:3n4,:)));
23	cb(o+n4+1:o+2n4,end-o+1:end) = fliplr(flipud(lln(n43+1:n4*4,:)));
24	cb(o+n42+1:o+3n4,end-o+1:end) = flipud(lln(1:n4,:));
25	cb(o+n43+1:o+4n4,end-o+1:end) = flipud(lln(2n4+1:3n4,:));
26
27	% now exchange regular part:
28	[nx,ny]=size(lla);
29	llb=NaNones(nx+2o,ny+o);
30	llb(o+1:o+nx,o+1:o+ny)=lla; % Interior
31	%b(o+1:o+nx,o+ny+(1:o))=a(:,ny:-1:ny-o+1); % N
32	%b(o+1:o+nx,1:o)=a(:,o:-1:1); % S
33	llb(o+nx+(1:o),:)=llb(o+1:o+o,:); % E
34	llb(1:o,:)=llb(o+nx-o+1:o+nx,:); % W
35
36	% put both parts together
37
38	b = [llb cb];
39
40
41