hep: Fixes bug in gamma_trace of sum of products containing GammaMatrix mixed with other symbols #23786

glenn-horton-smith · 2022-07-16T17:48:29Z

References to other Issues or PRs

Brief description of what is fixed or changed

physics.hep
- Fixed a bug in finding traces of sums of products of GammaMatrix mixed with other factors. (Strangely behaved gamma_trace (gamma matrix trace) #13636)

… of GammaMatrix mixed with other factors.

sympy-bot · 2022-07-16T17:48:30Z

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physics.hep
- Fixed a bug in finding traces of sums of products of GammaMatrix mixed with other factors. (Strangely behaved gamma_trace (gamma matrix trace) #13636) (#23786 by @glenn-horton-smith)

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#### References to other Issues or PRs

Fixes #13636 

#### Brief description of what is fixed or changed

<!-- BEGIN RELEASE NOTES -->
* physics.hep
  * Fixed a bug in finding traces of sums of products of GammaMatrix mixed with other factors. (#13636)
<!-- END RELEASE NOTES -->

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github-actions · 2022-07-16T20:45:12Z

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glenn-horton-smith · 2022-07-16T21:27:40Z

I don't know what to do about failing "test / optional-dependencies (3.11.0-alpha - 3.11, true) (pull_request)". It's completely unrelated to the change I made, and seems to be happening to everyone on all pull requests now.

oscarbenjamin · 2022-07-16T21:31:51Z

Yes, that's #23774.

It's fine if that test fails. It is not "required" to pass.

oscarbenjamin · 2022-07-24T20:42:38Z

.mailmap

@@ -588,6 +588,8 @@ Gilbert Gede <[email protected]> <[email protected]>
 Gilles Schintgen <[email protected]>
 Gina <[email protected]>
 Gleb Siroki <[email protected]>
+Glenn Horton-Smith <[email protected]>
+Glenn Horton-Smith <[email protected]> Glenn Horton-Smith <[email protected]>


I think only the first of these lines is needed. It doesn't look like the ksu.edu email is used in any of the commits. Did you add that because of an error reported by the mailmap script?

If you actually wanted your entry in the AUTHORS file to be recorded under ksu.edu then it should be the other way around i.e.:

Glenn Horton-Smith <[email protected]> Glenn Horton-Smith <[email protected]>

That way it is saying that the gmail address is an alias for the ksu address which should be the one recorded in the AUTHORS file and associated with these commits.

It's not needed for any current commit. I can remove the second line if you like. I only did it because I have "email = [email protected]" as a global setting on my work computer and I thought it might be useful in case I ever made a commit from work without remembering to set the email correctly.

The question is just which email address you would like to be recorded in AUTHORS. If you want it to be the gmail address then the above is fine.

Ah, ok. Yes, I want it to be the gmail address. Thanks for asking.

oscarbenjamin · 2022-07-24T20:43:03Z

sympy/physics/hep/tests/test_gamma_matrices.py

@@ -399,3 +400,25 @@ def test_gamma_matrix_trace():
    t = ps*ps*ps*ps*ps*ps*ps*ps
    r = gamma_trace(t)
    assert r.equals(4*p2*p2*p2*p2)
+
+def test_bug_13636():


Usually there should be two blank lines between top-level functions, classes etc.

This is fixed now.

oscarbenjamin · 2022-07-24T20:43:55Z

sympy/physics/hep/tests/test_gamma_matrices.py

+    assert ta.equals(
+        -16 * ki(i0) * ki(-i0) * pf(i1) * pi(-i1)
+        + 32 * ki(i0) * ki(i1) * pf(-i0) * pi(-i1)
+    )
+    assert tb.equals(-8 * x * ki(i0) * pf(-i0) * pi(i1) * pi(-i1))
+    assert t_a_plus_b.equals(ta + tb)


Does == not work here or does it need to use .equals?

Good question. I just checked, and indeed == does not work here. The .equals() function for tensor objects applies sympify and .cannon_bp to the tensor expression before comparing, while .eq is just Basic.eq, and is false for this comparison because the expression trees are not exactly identical. The other test functions such as test_gamma_matrix_trace() also use .equals().

Usually it is better to construct the exact expression for comparison in tests so that they can be compared with ==. Sometimes that is not be best option because the exact expression is confusing and does not display the intent of the test well.

I'm not sure what the preferred answer would be here. What exactly is the difference between the compared expressions? You can use srepr as one way to view the expression structure explicitly.

ta == 4*((-4)*ki(L_0)*ki(-L_0)*pf(L_1)*pi(-L_1) + 8*ki(L_0)*ki(L_1)*pf(-L_0)*pi(-L_1)) which is the same as the expression being tested against except for distribution of the factor of 4 over the coefficients. I can use the exact expression for the test, I don't mind.

tb and ta_plus_tb are the same as the expressions they are being compared against, so we could use == there with no problem.

This is fixed now.

oscarbenjamin · 2022-07-24T20:48:06Z

I can't personally verify the correctness of the code or the test from a mathematical perspective. Maybe @jksuom, @sami-b95 or @certik can?

If not then I'm happy to merge this but I'll wait to see if anyone can check it.

This particular module is not maintained which makes it difficult to merge PRs. As far as I know none of the people who actively merge PRs has expert knowledge of either the module or the subject matter. @glenn-horton-smith if you are interested in maintaining/improving this then that would be very welcome.

certik · 2022-07-24T21:02:28Z

I think this is correct. All it is doing is a test to make sure the sum of traces is the same as trace of the sum.

oscarbenjamin · 2022-07-24T21:22:33Z

Thanks @certik. Could you also check #23823?

I'll wait for @glenn-horton-smith to respond to my other comments but otherwise this is good to merge.

certik · 2022-07-24T22:10:56Z

Thanks @certik. Could you also check #23823?

Done.

oscarbenjamin · 2022-07-24T22:24:57Z

Thanks @certik!

Also some small whitespace changes for readability and style.

oscarbenjamin · 2022-07-28T08:46:34Z

The pypy failure and the 3.11 failure are both unrelated to the changes here.

glenn-horton-smith · 2022-07-29T22:56:09Z

Thanks @certik and @oscarbenjamin ! Have I missed responding to anything?

oscarbenjamin · 2022-07-29T23:48:04Z

Looks good to me.

Fixes issue sympy#13636 regarding handling traces of sums of products…

83a1172

… of GammaMatrix mixed with other factors.

glenn-horton-smith added 2 commits July 16, 2022 13:28

physics.hep: remove trailing space at end of docstring

f710565

Add myself to .mailmap

4b95864

oscarbenjamin reviewed Jul 24, 2022

View reviewed changes

oscarbenjamin mentioned this pull request Jul 24, 2022

Fix issue #23823 in physics.hep.gamma_matrices.kahane_simplify() #23824

Merged

Use == instead of .equals() for tensor comparison in tests.

f1d368f

Also some small whitespace changes for readability and style.

oscarbenjamin merged commit c9e427b into sympy:master Jul 29, 2022

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hep: Fixes bug in gamma_trace of sum of products containing GammaMatrix mixed with other symbols #23786

hep: Fixes bug in gamma_trace of sum of products containing GammaMatrix mixed with other symbols #23786

glenn-horton-smith commented Jul 16, 2022 •

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oscarbenjamin commented Jul 29, 2022

hep: Fixes bug in gamma_trace of sum of products containing GammaMatrix mixed with other symbols #23786

hep: Fixes bug in gamma_trace of sum of products containing GammaMatrix mixed with other symbols #23786

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glenn-horton-smith commented Jul 16, 2022 • edited Loading

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