Scheduler can exit with "The dependence graph is not a DAG."

[wvlothuizen]

this error was actually observed using PycQED test case Test_multi_qubit_oql_CC.test_two_qubit_parity_check (https://github.com/DiCarloLab-Delft/PycQED_py3/blob/develop/pycqed/tests/openql/test_multi_qubit_oql.py#L139)

details to reproduce:

• OpenQL https://github.com/DiCarloLab-Delft/OpenQL/commit/41df91c13db3cb9c070a2bfefbcdbb19115b0d39 (not yet upstreamed, but part of PR #360)
• PycQED commit: 470df5b2369060a2e1f17d87c1c527e6b54d7e26 (probably not so relevant because few changes occur)

[wvlothuizen]

This error still occurs after the recent refactor, i.e. in PR #360. Attached is the output of:

Zaphod-2:PycQED_py3 wouter$ pytest -v pycqed/tests/openql/ -k test_two_qubit_parity_check > test_two_qubit_parity_check.txt

The source of the test is at: https://github.com/DiCarloLab-Delft/PycQED_py3/blob/feature/DIOCal/pycqed/tests/openql/test_multi_qubit_oql.py#L139

the actual OpenQL calls at: https://github.com/DiCarloLab-Delft/PycQED_py3/blob/feature/DIOCal/pycqed/measurement/openql_experiments/multi_qubit_oql.py#L1358

test_two_qubit_parity_check.txt.zip

[wvlothuizen]

No longer observed in 0.10.x (using sch.ListSchedule)