function e = zcheck(x)
%ZCHECK	ZCHECK checks to see if a result is 0.
%	ZCHECK(X) is used to test that a result is 0
%	to within sqrt(eps) and issues an error if not.
%	

%	Copyright (c) 1990 by the MathWorks, Inc.
%	Written by John N. Little, 12-8-84.

if min(size(x)) == 0
	error([7,'Somebody returned a NULL matrix'])
end
if any(any(isnan(x)))
	error([7, 'Somebody returned a NaN'])
end
e = norm(x,1);
if (e > sqrt(eps))
	Residual_norm = e
	error([7, 'Residual greater than sqrt(Eps)'])
end
