qiskit/quantum_info/operators/operator.py
def _format_state(self, state):
        """Format input state so it is statevector or density matrix"""
        state = np.array(state)
        shape = state.shape
        ndim = state.ndim
        if ndim > 2:
            raise QiskitError('Input state is not a vector or matrix.')
        # Flatten column-vector to vector
        if ndim == 2:
            if shape[1] != 1 and shape[1] != shape[0]:
                raise QiskitError('Input state is not a vector or matrix.')
            if shape[1] == 1:
                # flatten colum-vector to vector
                state = np.reshape(state, shape[0])
        return state
def _format_state(self, state):
        """Format input state so it is statevector or density matrix"""
        state = np.array(state)
        shape = state.shape
        ndim = state.ndim
        if ndim > 2:
            raise QiskitError('Input state is not a vector or matrix.')
        # Flatten column-vector to vector
        if ndim == 2:
            if shape[1] != 1 and shape[1] != shape[0]:
                raise QiskitError('Input state is not a vector or matrix.')
            if shape[1] == 1:
                # flatten colum-vector to vector
                state = np.reshape(state, shape[0])
        return state
Format input state so it is statevector or density matrix