rcond — inverse condition number
rcond(X)
rcond(X) is an estimate for the reciprocal of the
condition of X in the 1-norm.
If X is well conditioned, rcond(X) is close to 1.
If not, rcond(X) is close to 0.
[r,z]=rcond(X) sets r to
rcond(X) and returns z such that
norm(X*z,1) = r*norm(X,1)*norm(z,1)
Thus, if rcond is small z is a vector in the kernel.