ECR implementation

[avbhadw]

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Context: Implementing ECR function as described here

Description of the Change: adding the operation (adjoint, eigenvalues, decomposition), adding support for qubit devices

Benefits:

Possible Drawbacks:

Related GitHub Issues:
Closes #2581

[antalszava]

Hi @avbhadw, thank you for the PR! 🙂 Let us know if this would be ready for review.

[codecov]

Codecov Report

Merging #2613 (e645941) into master (d31b6f7) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #2613   +/-   ##
=======================================
  Coverage   99.58%   99.58%           
=======================================
  Files         249      249           
  Lines       20202    20220   +18     
=======================================
+ Hits        20119    20137   +18     
  Misses         83       83           

Impacted Files	Coverage Δ
pennylane/devices/default_mixed.py	100.00% <ø> (ø)
pennylane/devices/default_qubit.py	100.00% <ø> (ø)
pennylane/ops/qubit/__init__.py	100.00% <ø> (ø)
pennylane/ops/qubit/non_parametric_ops.py	100.00% <100.00%> (ø)
pennylane/transforms/commutation_dag.py	100.00% <100.00%> (ø)

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[avbhadw]

Hey @antalszava I think this is ready for review. I did implement a function to calculate the power of the matrix but I am not sure how to test it, so I removed it. In my new commit there is no power function but when I run
python -m pytest tests/ops/qubit/test_non_parametric_ops.py
6 tests are failing, I think it is because this matrix uses complex numbers. Should I add back the power function?

Another issue I have is running make docs. I get the error below:
Extension error: You must configure the bibtex_bibfiles setting make[1]: *** [html] Error 2 make: *** [docs] Error 2

Is there a bibtex file I need to add?

Thanks!

[antalszava]

Hi @avbhadw, apologies for the delayed response here! I've been a bit unwell for the past couple of days.

The solution is looking great overall! 🎉 🙂 I've left a couple of minor comments.

For your questions:

1. The power method should be tested already based on your addition (see the related comment in the test file);
2. What if the sphinxcontrib-bibtex package is installed via pip install sphinxcontrib-bibtex.

Also, there seem to be some CI checks failing (apart form the test runners). Let me know and I could help with these if need be.

[avbhadw]

Hey @antalszava

I think I have resolved almost all of the reviews you have suggested(one unresolved, see above). I was having some trouble running make coverage (my computer does not have enough RAM for this to work), but I borrowed someone else's laptop (OS: Linux) and it worked. I believe I am no longer failing CI checks at least locally.

After trying your suggestion, I still have the same error with sphinxcontrib-bibtex. Another issue I have is installing the requirements to run make docs. I am using a MacOS and I get this error whenever I try to install torch
ERROR: Could not find a version that satisfies the requirement torch==1.9.0+cpu (from versions: 1.4.0, 1.5.0, 1.5.1, 1.6.0, 1.7.0, 1.7.1, 1.8.0, 1.8.1, 1.9.0, 1.9.1, 1.10.0, 1.10.1, 1.10.2, 1.11.0) ERROR: No matching distribution found for torch==1.9.0+cpu

From what I understand there isn't a torch package 1.9.0+cpu for macOS, I did remove the +cpu and install torch but I had an error when running make tests (short summary):

FAILED tests/docs/test_supported_confs.py::TestSupportedConfs::test_all_backprop_none_shots[wire_specs0-DensityMatrix-torch] - RuntimeError: unsupported input to tensordot, got dims=0 FAILED tests/docs/test_supported_confs.py::TestSupportedConfs::test_all_backprop_finite_shots[wire_specs0-DensityMatrix-torch] - RuntimeError: unsupported input to tensordot, got dims=0

I think once I am able to successfully run pip install -r doc/requirements.txt, the bibtex error should resolve.

I am thinking of trying to use docker but I am not sure if it would solve the problem.

[antalszava]

Hi @avbhadw, this looks good! 🎉

1-2 minor suggestions and it seems that the formatting is off (running black should help), afterwards, we'd merge this one.

As for the configuration issues, I'm not sure unfortunately. 🤔 Perhaps Docker would work, we do get some issues with Docker at times. For this PR, building the docs should be fine for now, the CI check seems good. 🙂

[avbhadw]

Hey @antalszava

I have implemented your suggestions and ran black (sorry I forgot). Thanks for being patient with me!

[avbhadw]

Hey @antalszava

I noticed black failing. I fixed it and pushed back up.
Sorry for the inconvenience

[antalszava]

Hi @avbhadw, no worries! 🙂 Thank you.

I'll be merging this PR soon. Thank you for your contribution! 👏