function	check_dcnots(vecs)

%Input is a matrix packed with 2 rows of unit 3d vectors.
%Input specifies a string of dressed cnots.
%This function checks that all the input vectors are unit vectors.

cols = columns(vecs);
if(rows(vecs)!=6)
	error("input doesn't have six rows.");
end
for c=1:cols
	r=1;
	while(r<5)
		if(abs(norm(vecs(r:r+2,c))-1)>1e-10)
			error("non-unit vector used to specify a dressed cnot");
		end
		r=r+3;
	end
end