Dimensions class #1996

Ericgig · 2022-09-19T20:58:02Z

Description

This is an overhaul of the dimensions based on the proposition by @jakelishman in #1476, replace #1826, which was done before merging master into dev.major and had conflicts.
As proposed, dimension objects singleton instances composed of map and spaces.

Dimensions used by Qobj are all represented by a map between 2 spaces:

ket: Dimensions(Field, Space)
bra: Dimensions(Space, Field)
oper: Dimensions(Space, Space)
...

This Dimension is the Map proposed by Jake, but ket are map from Field to Space and not Space themselves. Spaces come into multiple sub classes as proposed : Space, SuperSpace, Field, Compound, and EnrSpace. Splitting maps and spaces simplify spaces by not needing to have a dummy 2nd dims.

Dimensions can be initiated from a list and converted back to one. Field are automatically contracted: Compound(Field, Field) is a Field, same for maps. With the exceptions that Qobj with a shape of (1,1) with be a Dimensions(Field, Field) and not a Field.

Some previously valid and used list format are no longer accepted. Playing with of tensor of super operators, permute and reshuffle, you could make object with dims as [[[2, 2], [3, 3], [4, 4]], [[2, 2], [3, 3], [4, 4]]] which can be interpreted as the tensor of 3 super operators. But then [[[2, 2], [3, 3]], [[2, 2],[3, 3]]] can both be interpreted as tensor of super operator or super operator of tensor spaces, so :

[[[2, 2], [3, 3], [4, 4]], [[2, 2], [3, 3], [4, 4]]]: Error
[[[2, 2], [4, 4]], [[2, 2], [4, 4]]]: list representation of dimensions of to_super(tensor(oper, oper))
[[[2], [2], [3], [3]], [[2], [2], [3], [3]]]: list representation of dimensions of tensor(to_super(oper), to_super(oper))

Dimensions object have a type and shape set a initialization. There is a check when creating/ modifying a Qobj with between the data's shape and dims's shape and an error is raise when they are not matching.

Since operator-ket have a superrep, I added the superrep parameter to the Superspace instead of the dimensions, for now. But a better look at super operator representation is needed.

Qobj.dims take and return a list, keeping the dimension object internally. From there, minimal adjustment were made so test pass.

Related issues or PRs
Replace #1826

…rework

coveralls · 2023-02-13T21:24:25Z

coverage: 84.356% (-0.5%) from 84.849%
when pulling 80c6aad on Ericgig:dims.rework
into 4ce8829 on qutip:master.

hodgestar

I've done an initial review of the Qobj part and the basic metaclasses. Looking really great so far.

I asked quite a few questions around Qobj initialization. I'll continue the review of Field and the other space classes when I can.

hodgestar · 2023-08-03T16:16:38Z

qutip/core/qobj.py

+                and root_left * root_left != self._data.shape[1]
+            ):
+                raise ValueError(
+                    "cannot build superoperator from nonsquare subspaces"


This error message seems inaccurate now.

Not too sure how to properly explain it.
spre(NxM) @ spost(MxN) is fine but spre(NxN) @ spost(MxM) is not.
Both the input and output state of the super operator must be square matrix.

Is the idea here that the constructor will automatically square the dims if a superoperator is requested and the dims of the operator are supplied?

If so could we simplify this check by checking self._data.shape[0] == self._dims.shape[0] ** 2 and self._data.shape[1] == self._dims.shape[1] ** 2 and then squaring the supplied dims?

If this is not exactly what happens, perhaps there is another way to simplify the check since the detected dims and the supplied data should be related somehow.

If dims where not passed, dims where created to match the shape of the data.
If dims where passed, the check that their shape match the data shape was done in _initialize_data.

Hmm. The maybe the issue is that the check is sort of split between here and _initialize_data. Can we somehow make it so that the check happens in one place, or that it's repeated more fully here?

It looks like the relevant code is gone, but I don't know where the check went. How did you decide to resolve this?

I tried removing the type parameter and setter.
This mean that 1x1 are stuck at "scalar" without ways to change it and when creating super operators, setting dims properly is needed but were quite few places where it was not the case.

hodgestar · 2023-08-03T16:20:21Z

qutip/core/qobj.py

+                and self._data.shape != dims.shape
+                and self._data.shape == dims.shape[::-1]
+            ):
+                self._data = _data.transpose(self._data)


Should we not raise some sort of error here if the shape of the data and the shape of the supplied dims don't match?

It's for case where a vector is passed expecting a ket: Qobj([1, 2, 3], dims=[[3],[1]]).
Rereading it, the check is too general...

qutip/core/qobj.py

qutip/tests/core/test_qobj.py

qutip/core/dimensions.py

Co-authored-by: Simon Cross <hodgestar+github@gmail.com>

doc/apidoc/functions.rst

hodgestar

I've now reviewed all of the new dimensions code and the QobjEvo and Qobj changes.

It would be good to have tests for the new dimensions classes (in this PR) and documentation (so that I can see what the classes are intended to do and so that users can work with them, either in this PR or a follow-up one).

In general the approach looks great.

qutip/core/cy/qobjevo.pyx

hodgestar · 2023-11-08T10:54:28Z

qutip/core/cy/qobjevo.pyx

+
+    @property
+    def dims(self):
+        return self._dims.as_list()


Should we also have a means for the user to access the actual dims object?

To discuss, I do not like the list format much and would be fine with keeping it only for input and print.

I'd also be happy to only use the list format for input and printing the dims, but it would break some existing usage patterns (e.g. .dims[0]). This is v5 though, so maybe that is okay. Perhaps something we can discuss in the admin meeting or on the mailing list?

hodgestar · 2023-11-08T20:52:13Z

qutip/core/qobj.py

@@ -96,18 +82,16 @@ def _require_equal_type(method):
    @functools.wraps(method)
    def out(self, other):
        if other == 0:
-            return method(self, other)
+            return self.copy()


Calling .copy() here seems wrong unless the method is something where 0 is the identity?

_require_equal_type is used for __add__ and __sub__ only.

I don't think that is a good enough reason by itself to remove the call to method since it would break potential other users and nothing about the name of the decorator suggests it is not generally applicable.

hodgestar · 2023-11-08T21:20:19Z

qutip/core/qobj.py

+                and root_left * root_left != self._data.shape[1]
+            ):
+                raise ValueError(
+                    "cannot build superoperator from nonsquare subspaces"


Is the idea here that the constructor will automatically square the dims if a superoperator is requested and the dims of the operator are supplied?

If so could we simplify this check by checking self._data.shape[0] == self._dims.shape[0] ** 2 and self._data.shape[1] == self._dims.shape[1] ** 2 and then squaring the supplied dims?

If this is not exactly what happens, perhaps there is another way to simplify the check since the detected dims and the supplied data should be related somehow.

qutip/core/qobj.py

qutip/core/dimensions.py

hodgestar · 2023-11-09T13:48:10Z

qutip/core/dimensions.py

+        self.from_ = from_
+        self.to_ = to_
+        self.shape = to_.size, from_.size
+        self.issuper = from_.issuper or to_.issuper


Shouldn't it be an error is only one of from_.issuper or to_.issuper is true?

Not sure if we should block this.
There are users who use rectangular (super)-operator that I don't understand.
Maybe this could allow to define measurement operator that take dm and return ket etc.

My concern here is that .issuper is either true or false, but it's not clear to me whether something with from_.issuper is True and to_.issuper is False is actually a super operator or not.

qutip/core/dimensions.py

qutip/tests/core/test_dimensions.py

Co-authored-by: Simon Cross <hodgestar+github@gmail.com>

…ims.rework

hodgestar

@Ericgig Thanks for making the many rounds of changes and improvements. I'm pretty happy with how things look now and all the changes have made reviewing quite tricky. I propose that we merge this PR once you're happy and then make smaller issues for anything we want to clean up.

I'm happy to have another look at any final commits or things you're worried about in this PR though. Just ping me in the comments.

Ericgig and others added 8 commits August 25, 2022 16:44

Add Dimensions class to Qobj

bb9ecde

Merge branch 'dev.major' of https://github.com/qutip/qutip into dims.…

ea92672

…rework

Merge branch 'dev.major' of https://github.com/qutip/qutip into dims.…

d70bc88

…rework

simpler qobj init

027e65b

Fix doc build

a220e78

Add docstrings

07a0244

type as property

5ef0152

Merge remote-tracking branch 'upstream/master' into dims.rework

98a9c17

Ericgig changed the base branch from dev.major to master February 13, 2023 21:25

Add __all__ to dimensions.py

a975637

Ericgig requested a review from hodgestar February 14, 2023 16:55

Ericgig mentioned this pull request Feb 24, 2023

Support qutip-v5 qutip/qutip-qip#136

Merged

Merge branch 'master' of https://github.com/qutip/qutip into dims.rework

87d9592

Ericgig mentioned this pull request Mar 15, 2023

ENR states errors with v5 solvers #2122

Open

Ericgig added 3 commits June 28, 2023 13:48

Merge branch 'master' of https://github.com/qutip/qutip into dims.rework

c2ecbb3

Add towncrier entry

697d246

Merge branch 'master' of https://github.com/qutip/qutip into dims.rework

c8d5b97

hodgestar reviewed Aug 3, 2023

View reviewed changes

Ericgig and others added 4 commits August 4, 2023 11:31

Merge branch 'master' of https://github.com/qutip/qutip into dims.rework

92ce62e

Fix comments

f0f8e9a

Apply suggestions from code review

2f3974c

Co-authored-by: Simon Cross <hodgestar+github@gmail.com>

improve code climate

38800d8

hodgestar reviewed Nov 8, 2023

View reviewed changes

doc/apidoc/functions.rst Outdated Show resolved Hide resolved

hodgestar requested changes Nov 9, 2023

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Ericgig and others added 5 commits November 15, 2023 15:19

Apply suggestions from code review

009e605

Co-authored-by: Simon Cross <hodgestar+github@gmail.com>

Improve from comments

9c72295

Merge branch 'dims.rework' of https://github.com/Ericgig/qutip into d…

79e2d8d

…ims.rework

Merge branch 'master' of https://github.com/qutip/qutip into dims.rework

d039094

Remove old type check functions

05037cc

Ericgig and others added 5 commits November 17, 2023 10:42

start removing Qobj(type)

a93c7d5

start removing Qobj(type)

5c73919

Remove type setting

7aa4bf0

Rm type and reshape in Qobj.__init__

3fb1322

Stricker list format test

80c6aad

hodgestar approved these changes Nov 20, 2023

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Ericgig merged commit bc8b264 into qutip:master Nov 21, 2023
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Ericgig deleted the dims.rework branch November 21, 2023 15:12

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Dimensions class #1996

Dimensions class #1996

Ericgig commented Sep 19, 2022

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Dimensions class #1996

Dimensions class #1996

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Ericgig commented Sep 19, 2022

coveralls commented Feb 13, 2023 • edited

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coveralls commented Feb 13, 2023 •

edited