FusedGate.asmatrix breaks if gate appended is gates.Unitary created from a cupy ndarray

[renatomello]

Minimal code

from qibojit.backends import CupyBackend

from qibo import gates, matrices
from qibo.backends import NumpyBackend
from qibo.gates.special import FusedGate

nqubits = 1
I = matrices.I

for backend in [NumpyBackend, CupyBackend]:
    backend = backend()
    I = backend.cast(I, dtype=I.dtype)
    gate = FusedGate(*range(nqubits))
    gate.append(gates.Unitary(I, *range(nqubits)))
    gate = gate.asmatrix(backend)
    print(type(gate))

[renatomello]

There is a second issue that is probably related, which is FusedGate.asmatrix(backend) returns a numpy.ndarray when backend=CupyBackend(). E.g.

from qibo import gates
from qibojit.backends import CupyBackend
from qibo.gates.special import FusedGate

backend = CupyBackend()

gate = FusedGate(1)
gate.append(gates.I(0))
gate = gate.asmatrix(backend)
print(type(gate))

[renatomello]

@scarrazza the issue seems to come from the fact that the cupy backend does not have a matrices class (e.g. NumpyMatrices and TensorflowMatrices). In fact, any matrix coming from

CupyBackend().matrices

is of type numpy.ndarray instead of cupy.ndarray.

[scarrazza]

Thanks @renatomello, @andrea-pasquale could you please have look?