I'm trying to calculate the kernel of this matrix in Matlab with this command
null(A)
But I receive this error
Empty matrix: 2-by-0
\begin{bmatrix}
5&-3\\
1&1\\
1&-1\\
\end{bmatrix}
I don't understand why I can't calculate the kernel of this matrix in Matlab
That is not an error message.
Z = null(A) is an orthonormal basis for the null space of A obtained from the singular value decomposition, in this case, the dimension of the nullspace is $0$. Your matrix has full column rank as we can see that the columns are not multiple of each other.