Error in check for the normalizer method of a single operator generating set

[dsvandet]

Steps to reproduce the problem

import qiskit_qec.linear.symplectic as symp
a = Pauli('XX')
symp.normalizer(a.matrix)

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
Untitled-1.ipynb Cell 10' in <cell line: 1>()
----> [1](vscode-notebook-cell:Untitled-1.ipynb?jupyter-notebook#ch0000009untitled?line=0) symp.normalizer(a.matrix)

File ~/Software/Public/working/qiskit-qec/qiskit_qec/linear/symplectic.py:2049, in normalizer(matrix, x, z, min_gen)
   [2047](file:///Users/dsvandet/Software/Public/working/qiskit-qec/qiskit_qec/linear/symplectic.py?line=2046) if min_gen:
   [2048](file:///Users/dsvandet/Software/Public/working/qiskit-qec/qiskit_qec/linear/symplectic.py?line=2047)     matrix = min_generating(matrix)
-> [2049](file:///Users/dsvandet/Software/Public/working/qiskit-qec/qiskit_qec/linear/symplectic.py?line=2048) if is_stabilizer_group(matrix):
   [2050](file:///Users/dsvandet/Software/Public/working/qiskit-qec/qiskit_qec/linear/symplectic.py?line=2049)     return _normalizer_abelian_group(matrix)
   [2051](file:///Users/dsvandet/Software/Public/working/qiskit-qec/qiskit_qec/linear/symplectic.py?line=2050) else:

File ~/Software/Public/working/qiskit-qec/qiskit_qec/linear/symplectic.py:1191, in is_stabilizer_group(matrix)
   [1189](file:///Users/dsvandet/Software/Public/working/qiskit-qec/qiskit_qec/linear/symplectic.py?line=1188) if not is_symplectic_matrix_form(matrix):
   [1190](file:///Users/dsvandet/Software/Public/working/qiskit-qec/qiskit_qec/linear/symplectic.py?line=1189)     raise QiskitError("Input matrix not a GF(2) symplectic matrix")
-> [1191](file:///Users/dsvandet/Software/Public/working/qiskit-qec/qiskit_qec/linear/symplectic.py?line=1190) return all_commute(matrix)

File ~/Software/Public/working/qiskit-qec/qiskit_qec/linear/symplectic.py:54, in all_commute(matrix)
     [27](file:///Users/dsvandet/Software/Public/working/qiskit-qec/qiskit_qec/linear/symplectic.py?line=26) r"""Determines if each possible pair of different rows of the
     [28](file:///Users/dsvandet/Software/Public/working/qiskit-qec/qiskit_qec/linear/symplectic.py?line=27) GF(2) symplectic matrix have zero symplectic product. If the rows represent
     [29](file:///Users/dsvandet/Software/Public/working/qiskit-qec/qiskit_qec/linear/symplectic.py?line=28) Pauli operators then the this method deterimes if the operators
   (...)
     [51](file:///Users/dsvandet/Software/Public/working/qiskit-qec/qiskit_qec/linear/symplectic.py?line=50)     True
     [52](file:///Users/dsvandet/Software/Public/working/qiskit-qec/qiskit_qec/linear/symplectic.py?line=51) """
     [53](file:///Users/dsvandet/Software/Public/working/qiskit-qec/qiskit_qec/linear/symplectic.py?line=52) test_mat = symplectic_product(matrix, matrix)
---> [54](file:///Users/dsvandet/Software/Public/working/qiskit-qec/qiskit_qec/linear/symplectic.py?line=53) return not test_mat.any()

AttributeError: 'int' object has no attribute 'any'

What is the current behavior?

As above.

What is the expected behavior?

Should return the normalizer of the group generated by $X_0X1$ in the 2-qubit Pauli Group.

How to fix

The problem lies with the check in the normalizer method checking that the input matrix represents a set of commuting operators. The check runs symplectic_product(matrix, matrix) but since matrix is a vector in this example the current returned result is an integer and thus lacks an any method.

Fix: Apply np.asarray() to the result of the symplectic product

Unit tests

I unit test should be added to include this case - single generator (single row matrix)