[TEMPLATES] Rewrite state preparation templates as operations #1190

mariaschuld · 2021-04-06T10:02:40Z

This is the third PR to refactor the templates (following 1156 and 1163).

Changes:

Templates are turned into operations, so that the decomposition is executed in the expand function.
The pre-processing was moved into the __init__ function.
The tests were moved into a separate file.
Docstrings were improved.
If the template takes weights, a method to return the shape of the weights was added.

Drawbacks:
The existing MottonenStatePreparation gradient test is insufficient, and it turns out that for most cases gradients do not yet work. However, this is a major task and should be done in a separate PR.

github-actions · 2021-04-06T10:03:00Z

Hello. You may have forgotten to update the changelog!
Please edit .github/CHANGELOG.md with:

A one-to-two sentence description of the change. You may include a small working example for new features.
A link back to this PR.
Your name (or GitHub username) in the contributors section.

mariaschuld · 2021-04-06T10:12:53Z

pennylane/templates/state_preparations/mottonen.py

+    .. warning::
+
+        Due to non-trivial classical processing of the state vector,
+        this template is not always fully differentiable.


I added this warning for now.

mariaschuld · 2021-04-06T11:52:35Z

pennylane/tape/tape.py

@@ -1103,7 +1103,9 @@ def to_openqasm(self, wires=None, rotations=True):
                    op.inv()

        # decompose the queue
-        operations = tape.expand(stop_at=lambda obj: obj.name in OPENQASM_GATES).operations
+        operations = tape.expand(
+            depth=10, stop_at=lambda obj: obj.name in OPENQASM_GATES


We have one more level of "nesting", so need to define depth here.

mariaschuld · 2021-04-06T11:53:10Z

tests/templates/test_subroutines.py

@@ -1572,7 +1572,7 @@ def test_phase_estimated_two_qubit(self):
                )
                qml.probs(estimation_wires)

-            tape = tape.expand()
+            tape = tape.expand(depth=2)


Same problem as above...

mariaschuld · 2021-04-06T11:54:39Z

tests/tape/test_tape.py

@@ -728,7 +729,7 @@ def test_nesting_and_decomposition(self):
            qml.probs(wires=0), qml.probs(wires="a")

        new_tape = tape.expand()
-        assert len(new_tape.operations) == 5
+        assert len(new_tape.operations) == 4


I thought here we do not have to expand to higher depth, but can just adjust the count...

mariaschuld · 2021-04-06T11:55:14Z

pennylane/tape/tape.py

@@ -1103,7 +1103,9 @@ def to_openqasm(self, wires=None, rotations=True):
                    op.inv()

        # decompose the queue
-        operations = tape.expand(stop_at=lambda obj: obj.name in OPENQASM_GATES).operations
+        operations = tape.expand(
+            depth=2, stop_at=lambda obj: obj.name in OPENQASM_GATES


We have one more level of nesting, so need to increase the depth here.

codecov · 2021-04-06T12:08:32Z

Codecov Report

Merging #1190 (62c6b43) into master (fd99be7) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1190   +/-   ##
=======================================
  Coverage   98.12%   98.12%           
=======================================
  Files         145      145           
  Lines       10893    10903   +10     
=======================================
+ Hits        10689    10699   +10     
  Misses        204      204

Impacted Files	Coverage Δ
pennylane/tape/tape.py	`98.51% <100.00%> (ø)`
.../state_preparations/arbitrary_state_preparation.py	`100.00% <100.00%> (ø)`
pennylane/templates/state_preparations/basis.py	`100.00% <100.00%> (ø)`
pennylane/templates/state_preparations/mottonen.py	`100.00% <100.00%> (ø)`

Continue to review full report at Codecov.

Legend - Click here to learn more
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albi3ro

Do we need to catch if state preparation is not occurring at the beginning of a circuit on a 00000... state?

I tested

@qml.qnode(dev)
def circuit():
    qml.PauliX(wires=(0))
    qml.templates.state_preparations.basis.BasisStatePreparation([1,0,0], wires=(0,1,2))
    return qml.state()

and that lead to non-intuitive behaviour.

I left a lot of comments, but most of them are just suggestions.

The things that should really be changed are:

placing test_basis_state_prep.TestInputs.test_exception_wrong_dim in the correct file
using pytest.importorskip in interface tests
docstring for ArbitraryStatePreparation

pennylane/templates/state_preparations/arbitrary_state_preparation.py

pennylane/templates/state_preparations/basis.py

albi3ro · 2021-04-06T21:01:15Z

tests/templates/test_state_preparations/test_arbitrary_state_prep.py

+        assert shape == expected_shape
+
+
+def circuit_template(weights):


Should these be fixtures? Just curious.

I think it's ok if they are just functions defined somewhere...since they change in every test, so it would be no use to make them global fixtures...Or did I understand wrong?

I am never sure if I should put them into the test class, but I find it so ugly to refer to them with self...

tests/templates/test_state_preparations/test_arbitrary_state_prep.py

tests/templates/test_state_preparations/test_basis_state_prep.py

pennylane/templates/state_preparations/mottonen.py

…tion.py Co-authored-by: Christina Lee <christina@xanadu.ai>

…e into rewrite-state-preps

…e-state-preps

mariaschuld · 2021-04-07T07:14:59Z

Thanks @albi3ro for your great review!

The bug about BasisStatePreparation not being checked for being the first operation in a circuit is indeed confusing. Can we solve this in a separate issue though, since it would be a breaking change? I will open one!

albi3ro

Looks great!

It was great to learn about a new section of code and thanks for answering all my questions and nitpicks 👍

mariaschuld added 4 commits April 6, 2021 10:46

rewrite arbitrary state prep

a96a8ec

rewrite arbitrary state prep

aecef9b

backup

972c6b1

all tests passing

769ade9

improve docstrings

22bf2cd

mariaschuld commented Apr 6, 2021

View reviewed changes

polish

66b9df8

mariaschuld requested review from albi3ro and antalszava April 6, 2021 10:17

mariaschuld added 3 commits April 6, 2021 12:19

black

731e7c3

fix qasm

ea1fe7e

black

eb0c9bf

mariaschuld commented Apr 6, 2021

View reviewed changes

adjust expansion depths

f087325

mariaschuld commented Apr 6, 2021

View reviewed changes

black

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albi3ro requested changes Apr 6, 2021

View reviewed changes

mariaschuld and others added 5 commits April 7, 2021 07:55

Update pennylane/templates/state_preparations/arbitrary_state_prepara…

125a0c9

…tion.py Co-authored-by: Christina Lee <christina@xanadu.ai>

applied code review

bdd2cc3

Merge branch 'rewrite-state-preps' of github.com:PennyLaneAI/pennylan…

76cbcfa

…e into rewrite-state-preps

Merge branch 'master' of github.com:PennyLaneAI/pennylane into rewrit…

dd74394

…e-state-preps

fix test imports in embeddings tests

f99adb6

improve test

a639ccd

mariaschuld requested a review from albi3ro April 7, 2021 07:28

updated changelog

62c6b43

mariaschuld mentioned this pull request Apr 7, 2021

[TEMPLATES] Rewrite subroutines as operations #1192

Merged

albi3ro approved these changes Apr 7, 2021

View reviewed changes

mariaschuld merged commit 8480ab7 into master Apr 8, 2021

mariaschuld deleted the rewrite-state-preps branch April 8, 2021 06:37

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[TEMPLATES] Rewrite state preparation templates as operations #1190

[TEMPLATES] Rewrite state preparation templates as operations #1190

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		assert shape == expected_shape


		def circuit_template(weights):

[TEMPLATES] Rewrite state preparation templates as operations #1190

[TEMPLATES] Rewrite state preparation templates as operations #1190

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