DDSim has segmentation fault when running QAOA and Portfolio Optimization with QAOA circuits from MQT Bench

[rentristandelacruz]

mqt.ddsim version

1.17.2

OS

Linux Mint 21.1

Python version

3.10

C++ compiler

11.3.0

Additional environment information

No response

Description

I am simulating some circuits from the MQT Bench (https://www.cda.cit.tum.de/mqtbench/) using DDSim. Specifically, I am the using qasm_simulator backend and for the circuits I download a set of target-independent (compiler: qiskit) qasm files from the MQT Bench web page. I am currently using the DDSim v1.17.2.

When I recently run a QAOA or Portfolio Optimization with QAOA circuits (e.g. portfolioqaoa_indep_qiskit_3.qasm, qaoa_indep_qiskit_3.qasm.) using the qasm_simulator backend I encounter segmentation faults. I did not encounter the segmentation fault issue with the other circuits from the set (i.e. Deutsch-Jozsa, GHZ, Grover's, etc).

I was simulating the same set of circuits a couple of months ago and I did not encounter the segmentation fault when running the QAOA-related circuits. Upon checking, I was using DDSim v1.13.1. I prepared different Python virtual environments and installed different versions of mqt.ddsim. The segmentation fault when running QAOA-related circuits started occurring in version 1.17.0. Version 1.16.0 can run the QAOA and Portfolio Optimization with QAOA circuits without the segmentation fault occurring.

Expected behavior

No response

How to Reproduce

1. Create a Python virtual environment and install mqt.ddsim v.1.17.0.

• mdkir ddsim-1.17.0
• python3.10 -m venv ddsim-1.17.0
• source ddsim-1.17.0/bin/activate
• pip install --force-reinstall -v "mqt.ddsim==1.17.0"

2. Download one qasm QAOA circuit and one Portfolio Optimization with QAOA circuit (target-independet, compiler:qiskit ) from MQT Bench page (https://www.cda.cit.tum.de/mqtbench/). e.g. portfolioqaoa_indep_qiskit_3.qasm, qaoa_indep_qiskit_3.qasm.
3. Create a Python script, used the ddsim qasm_simulator backend and simulate both qaoa and portfolioqaoa circuit.
   e.g. script:

import sys                                                                                                                              
from qiskit import *                                                                                 
from mqt    import ddsim                                                                                                                                                                                  
qasmFilename     = sys.argv[1]                                                                       
quantumCircuit   = QuantumCircuit.from_qasm_file(sys.argv[1])                                        
backendSimulator = ddsim.DDSIMProvider().get_backend("qasm_simulator")                               
myJob            = execute(quantumCircuit, backendSimulator)                                         
print(myJob.result()) 

[hillmich]

Thanks for bringing up this issue. I can reproduce the segmentation fault locally but unfortunately I did not find the cause yet.

Some observations:

1. The circuit runs fine when passing the file to the c++ command line version.
2. The circuit runs fine in python when removing the rzz gates.
3. In principle the rzz should work as they do in test_standalone_simulator.py (test_native_two_qubit_gates)

[hillmich]

The latest commit to the main branch should fix the problem. Could you test this as well? I will add a new test for the fix later and create a new release.

[rentristandelacruz]

The update works. I no longer encounter segmentation faults when running QAOA-related circuits using the qasm_simulator backend. Thank you for the quick fix.

Some additional information: I'm running MQT Bench's circuits on the different DDSim backends including hybrid_qasm_simulator and path_sim_qasm_simulator. I'm encountering something QAOA-related again but this time when using hybrid_qasm_simulator and path_sim_qasm_simulator backends.

When running a QAOA circuit using the hybrid_qasm_simulator (in either dd or amplitude mode) , the following log appears: ValueError: Only StandardOperations are supported for now.

When running a QAOA circuit using the path_sim_qasm_simulator (in any of the modes), the following log appears: ValueError: DD for non-unitary operation not available!

Is this expected behavior or is it a possible issue? (maybe related to rzz gates again?) I can open a separate issue with replication procedure if you think this is a bug. Thanks!

[hillmich]

The hybrid_qasm_simulator and path_sim_qasm_simulator only support standard operations, i.e. unitary operations. For the QAOA example you provided you should be fine with removing the measurements at the end.

In fact, the simulator should automatically remove the measurements at the end of the circuit but I guess the barriers are blocking the removal. Maybe something @burgholzer can also comment on?

[burgholzer]

I am fairly sure that the barrier statements are the problem.
IIRC measurements at the end are already removed automatically in both of these simulators.
Should be an easy fix by just skipping over barrier statements.

@rentristandelacruz would you mind creating a separate issue for that?

[rentristandelacruz]

I am fairly sure that the barrier statements are the problem. IIRC measurements at the end are already removed automatically in both of these simulators. Should be an easy fix by just skipping over barrier statements.

@rentristandelacruz would you mind creating a separate issue for that?

I created a separate issue for this.