function [msg,nx,ny] = xyuvcheck(x,y,u,v)
%XYUVCHECK  Check arguments to 2D vector data routines.
%   [MSG,X,Y] = XYZCHK(X,Y,U,V) checks the input aguments
%   and returns either an error message in MSG or valid X,Y.

%   Copyright 1984-2002 The MathWorks, Inc. 
%   $Revision: 1.6 $  $Date: 2002/06/17 13:37:45 $

msg = '';
nx = x;
ny = y;

sz = size(u);
if ~isequal(size(v), sz)
  msg='U,V must all be the same size.';
  return
end

if ndims(u)~=2
  msg='U,V must all be a 2D arrays.';
  return
end
if min(sz)<2
  msg = 'U,V must all be size 2x2x2 or greater.'; 
  return
end

nonempty = ~[isempty(x) isempty(y)];
if any(nonempty) & ~all(nonempty)
  msg = 'X,Y must both be empty or both non-empty.';
  return;
end

if ~isempty(nx) & ~isequal(size(nx), sz)
  nx = nx(:);
  if length(nx)~=sz(2)
    msg='The size of X must match the size of U or the number of columns of U.';
    return
  else
    nx = repmat(nx',[sz(1) 1]);
  end
end

if ~isempty(ny) & ~isequal(size(ny), sz)
  ny = ny(:);
  if length(ny)~=sz(1)
    msg='The size of Y must match the size of U or the number of rows of U.';
    return
  else
    ny = repmat(ny,[1 sz(2)]);
  end
end