Construct multi-qubit Pauli terms and sums from strings #984

jlbosse · 2019-08-31T07:07:54Z

Description

Added PauliSum.from_compact_str() and PauliSum.compact_str() in analogy to PauliTerm.from_compact_str() and PaulTerm.compact_str().
Added support for multi-qubit operators to PauliTerm.from_compact_str().
Added corresponding tests.

This resolves #977 mostly (except for the question, whether init() should also be changed).

Checklist

The above description motivates these changes.
There is a unit test that covers these changes.
All new and existing tests pass locally and on Semaphore.
test_examples.test_quantum_die fails, but since I ddin't touch anything remotely related I
am sure I can shift the blame
Parameters have type hints with PEP 484 syntax.
None of the surrounding code has type hints, so I refrained from adding them.
Functions and classes have useful sphinx-style docstrings.
(New Feature) The docs have been updated accordingly.
(Bugfix) The associated issue is referenced above using
auto-close keywords.
The changelog is updated,
including author and PR number (@username, gh-xxx).

Added support for multi-qubit strings to PauliTerm.from_compact_str Added Tests for all of the above changed: pyquil/paulis.py changed: pyquil/tests/test_paulis.py changed: pyquil/tests/test_paulis_with_placeholders.py

changed: pyquil/tests/test_paulis.py changed: pyquil/tests/test_paulis_with_placeholders.py

@msohaibalam

and the tests. Made the syntactical changes requested by @msohaibalam Zum Commit vorgemerkte Änderungen: geändert: pyquil/paulis.py geändert: pyquil/tests/test_paulis.py geändert: pyquil/tests/test_paulis_with_placeholders.py

Fixed the dimensions of the resulting matrices, s.t. it produces the same results as pyquil.unitary_tools.lifted_pauli

- Added PauliSum.from_compact_str() - Added support for multiqubit strings to PauliTerm.from_compact_str() - Added PauliSum.compact_str() changed: paulis.py changed: tests/test_paulis.py changed: tests/test_paulis_with_placeholders.py

changed: CHANGELOG.md changed: docs/source/apidocs/pauli.rst

appleby

Small docstring typo. Otherwise looks reasonable to me.

pyquil/paulis.py

appleby

I don't have an opinion on the __init__ question, but otherwise lgtm

karalekas

@jlbosse Thanks for the PR! I think the scope of this looks great. However, parsing magic strings can get a little hairy. For example, the following does not work:

In [21]: print(PauliSum.from_compact_str('X0 + X1'))
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-21-b4e8046c399b> in <module>
----> 1 print(PauliSum.from_compact_str('X0 + X1'))

~/code/rigetti/github/pyquil/pyquil/paulis.py in from_compact_str(cls, str_pauli_sum)
    704         str_terms = re.split(r'\+(?![^(]*\))', str_pauli_sum)
    705         str_terms = [s.strip() for s in str_terms]
--> 706         terms = [PauliTerm.from_compact_str(term) for term in str_terms]
    707         return cls(terms)
    708

~/code/rigetti/github/pyquil/pyquil/paulis.py in <listcomp>(.0)
    704         str_terms = re.split(r'\+(?![^(]*\))', str_pauli_sum)
    705         str_terms = [s.strip() for s in str_terms]
--> 706         terms = [PauliTerm.from_compact_str(term) for term in str_terms]
    707         return cls(terms)
    708

~/code/rigetti/github/pyquil/pyquil/paulis.py in from_compact_str(cls, str_pauli_term)
    359         """
    360         # split into coefficient and operator
--> 361         str_coef, str_op = str_pauli_term.split('*', maxsplit=1)
    362
    363         # parse the coefficient

ValueError: not enough values to unpack (expected 2, got 1)

Granted, this example is due to the fact that print(PauliTerm.from_compact_str('X0')) doesn't work, but there are other "reasonable-looking" strings that you can put in that spit out a confusing error. Thus, I think it would be best to expand upon your unit test, and include every flavor of compact string you can think of. For those that should actually result in an error, we should catch that and return an error message that gives the user a sense of what to do next. Let me know if that makes sense -- happy to add more detail.

Some additional examples:

this should probably error but doesn't

In [24]: print(PauliTerm.from_compact_str('1+1j*X0'))
(1+1j)*X0

this should probably collect terms

In [29]: print(PauliSum.from_compact_str("(1.0+0j)*X0 + (1.0+0j)*Y0 + 1*X0"))
(1+0j)*X0 + (1+0j)*Y0 + (1+0j)*X0

this should probably tell you "A" is the problem

In [30]: PauliSum.from_compact_str("(1.0+0j)*X0 + (1.0+0j)*A0")
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-30-e717615331a7> in <module>
----> 1 PauliSum.from_compact_str("(1.0+0j)*X0 + (1.0+0j)*A0")

~/code/rigetti/github/pyquil/pyquil/paulis.py in from_compact_str(cls, str_pauli_sum)
    704         str_terms = re.split(r'\+(?![^(]*\))', str_pauli_sum)
    705         str_terms = [s.strip() for s in str_terms]
--> 706         terms = [PauliTerm.from_compact_str(term) for term in str_terms]
    707         return cls(terms)
    708

~/code/rigetti/github/pyquil/pyquil/paulis.py in <listcomp>(.0)
    704         str_terms = re.split(r'\+(?![^(]*\))', str_pauli_sum)
    705         str_terms = [s.strip() for s in str_terms]
--> 706         terms = [PauliTerm.from_compact_str(term) for term in str_terms]
    707         return cls(terms)
    708

~/code/rigetti/github/pyquil/pyquil/paulis.py in from_compact_str(cls, str_pauli_term)
    378         str_op = re.sub(r'\*', '', str_op)
    379         if not re.match(r'^(([XYZ])(\d+))+$', str_op):
--> 380             raise ValueError(f"Could not parse pauli string {str_pauli_term}")
    381
    382         for factor in re.finditer(r'([XYZ])(\d+)', str_op):

ValueError: Could not parse pauli string (1.0+0j)*A0

Many (if not all) of these are errors that existed before you opened your PR, so if you'd rather just catch them in your tests as expected errors, open an issue, and leave them for a later PR (as to not blow up the scope of your work) that is totally fine with me. In fact, that might be the best course of action. Let me know what you think! 😃

karalekas · 2019-09-15T19:10:22Z

As for __init__, let's leave that question for another PR. 👍

Committed changes: changed: paulis.py changed: tests/test_paulis.py

jlbosse · 2019-09-18T04:43:59Z

@karalekas Thanks for pointing out the manifold ways the user could specify unparsable strings. I added checks for each part of the string now that point at the exact part where things became unparsable.

For the case "(1.0+0j)*X0 + (1.0+0j)*Y0 + 1*X0" I added a simple .simplify() before return.
"(1.0+0j)*A0" and "X0 + X1" now throw more informative exceptions.
"1+1j*X0" is still considered equivalent to "(1+1j)*X0". Should I add another check, that '+' only shows up inside parenthesis when part of a pauli_term_str? Note, that this is only potentially confusing when passed to PauliTerm.from_compact_str(). PauliSum.from_compact_str(), on the other hand, will choke on "1+1j*X0" and raise a value error telling you what went wrong.

karalekas

Thanks for adding all those tests! I think this is nearly ready, but I think that the test_pauli_sum_from_str could be expanded as well. Could you test a couple more pauli sum strings that should parse correctly, as well as test the simplification component?

- Test that simplification works correctly - Test that PauliSums of length 1 work correctly - Test that strings containing the identity work correctly Changed files: changed: tests/test_paulis.py

jlbosse · 2019-09-19T03:04:09Z

Done! I added tests for the simplification part, strings containing the identity and sums of length one.

karalekas

Some small fixes to the changelog entry -- also please move it up to the "Improvements and Changes" section for v2.12, instead of v2.11. Probably want to rebase off of master too.

CHANGELOG.md

Co-Authored-By: Peter Karalekas <peter@rigetti.com>

jlbosse · 2019-09-20T01:16:13Z

Incorporated the Changelog changes (and clearly didn't write that fact into the changelog, otherwise I would still be stuck in a recursive loop without exit condition). Rebasing off master has been done commit e761981.

karalekas

LGTM

karalekas · 2019-09-20T17:35:16Z

@jlbosse Congrats on your first PR contribution to pyQuil! :)

jlbosse added 10 commits March 29, 2019 15:25

Added PauliTerm.matrix() and PauliSum.matrix() methods

2d6e7f7

Added support for multi-qubit strings to PauliTerm.from_compact_str Added Tests for all of the above changed: pyquil/paulis.py changed: pyquil/tests/test_paulis.py changed: pyquil/tests/test_paulis_with_placeholders.py

fixed formatting to be flake8 compliant

49da535

changed: pyquil/tests/test_paulis.py changed: pyquil/tests/test_paulis_with_placeholders.py

fixed formatting

7c0612f

Merge branch 'master' of https://github.com/rigetti/pyquil

553c452

Added @msohaibalams suggestions.

cad37a4

Fixed the dimensions of the resulting matrices, s.t. it produces the same results as pyquil.unitary_tools.lifted_pauli

Merge branch 'master' of https://github.com/rigetti/pyquil

91ee70f

Added better string conversion to paulis.py

9f27c7e

- Added PauliSum.from_compact_str() - Added support for multiqubit strings to PauliTerm.from_compact_str() - Added PauliSum.compact_str() changed: paulis.py changed: tests/test_paulis.py changed: tests/test_paulis_with_placeholders.py

Added checks to PauliTerm.from_list_back

5aa27eb

Updated the changelog and docs

3f5a7c6

changed: CHANGELOG.md changed: docs/source/apidocs/pauli.rst

jlbosse requested a review from a team as a code owner August 31, 2019 07:07

jlbosse added 2 commits August 31, 2019 15:12

fixed regex formatting

2891407

corrected PR number in Changelog.md

5e7a47e

appleby reviewed Sep 6, 2019

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Fixed a docstring typo in paulis.py

917db7d

appleby approved these changes Sep 6, 2019

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karalekas suggested changes Sep 15, 2019

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jlbosse added 2 commits September 18, 2019 11:17

Merge remote-tracking branch 'rigetti/master' into from_compact_str

e761981

Added more tests and assertions to catch wrong pauli strings.

f71a67c

Committed changes: changed: paulis.py changed: tests/test_paulis.py

karalekas suggested changes Sep 18, 2019

View reviewed changes

Added more tests for PauliSum.from_compact_str()

6e3c99b

- Test that simplification works correctly - Test that PauliSums of length 1 work correctly - Test that strings containing the identity work correctly Changed files: changed: tests/test_paulis.py

added whitespace around operators

63641b6

karalekas suggested changes Sep 19, 2019

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This was referenced Sep 19, 2019

Allow for Pauli strings that have only operators #1007

Open

Improve error messaging around Pauli string parsing #1008

Open

jlbosse and others added 2 commits September 20, 2019 09:09

Update CHANGELOG.md

6b0bd42

Co-Authored-By: Peter Karalekas <peter@rigetti.com>

Update CHANGELOG.md

e5ee352

Co-Authored-By: Peter Karalekas <peter@rigetti.com>

jlbosse and others added 2 commits September 20, 2019 09:10

Update CHANGELOG.md

07d6882

Co-Authored-By: Peter Karalekas <peter@rigetti.com>

updated Changelog and moved the PR 984 to v2.12

d91b12e

karalekas changed the title ~~Added PauliSum.from_compact_str() and updated PaulTerm.from_compact_str()~~ Construction of multi-qubit Pauli terms and sums from strings Sep 20, 2019

karalekas changed the title ~~Construction of multi-qubit Pauli terms and sums from strings~~ Construct multi-qubit Pauli terms and sums from strings Sep 20, 2019

karalekas approved these changes Sep 20, 2019

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karalekas merged commit 9bdbd71 into rigetti:master Sep 20, 2019

karalekas added this to the v2.12 milestone Sep 20, 2019

karalekas added the enhancement ✨ A request for a new feature. label Sep 20, 2019

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Construct multi-qubit Pauli terms and sums from strings #984

Construct multi-qubit Pauli terms and sums from strings #984

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Construct multi-qubit Pauli terms and sums from strings #984

Construct multi-qubit Pauli terms and sums from strings #984

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