Bug when loading a process tensor from file

[gefux]

I've found a bug when loading a process tensor with non-diagonal coupling from a file.

Here is a (minimal) failing example:

import oqupy

TEMP_FILE = "./temp-process-tensor.hdf5"

system = oqupy.System(oqupy.operators.sigma("x"))
initial_state = oqupy.operators.spin_dm("z+")
correlations = oqupy.PowerLawSD(
    alpha=0.3,
    zeta=1.0,
    cutoff=5.0,
    cutoff_type="exponential",
    temperature=0.2,
    name="ohmic")bath = oqupy.Bath(
    0.5*oqupy.operators.sigma("x"),
    correlations)
tempo_params = oqupy.TempoParameters(
    dt=0.1,
    dkmax=5,
    epsrel=10**(-5))
pt = oqupy.pt_tempo_compute(
    bath,
    start_time=0.0,
    end_time=0.3,
    process_tensor_file=TEMP_FILE,
    overwrite=True,
    parameters=tempo_params)
del pt

pt = oqupy.import_process_tensor(TEMP_FILE, process_tensor_type="file")

This is the output:

--> PT-TEMPO computation:
100.0%    2 of    2 [########################################] 00:00:00
Elapsed time: 0.0s
Traceback (most recent call last):
  File "./examples/fail.py", line 33, in <module>
    pt = oqupy.import_process_tensor(TEMP_FILE, process_tensor_type="file")
  File "./oqupy/process_tensor.py", line 729, in import_process_tensor
    pt_file = FileProcessTensor(mode="read", filename=filename)
  File "./oqupy/process_tensor.py", line 457, in __init__
    dictionary = self._read_file(filename)
  File "./oqupy/process_tensor.py", line 536, in _read_file
    if transform_in == 0.0:
ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()