Fix PolyElement.as_expr()

[skieffer]

References to other Issues or PRs

Fixes #24538

Brief description of what is fixed or changed

Make PolyElement.as_expr() accept symbols.

Release Notes

• polys
  • Repaired a bug with PolyElement.as_expr(), so that it now accepts symbols.

[sympy-bot]

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• polys
  • Repaired a bug with PolyElement.as_expr(), so that it now accepts symbols. (#24539 by @skieffer)

This will be added to https://github.com/sympy/sympy/wiki/Release-Notes-for-1.12.

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#### References to other Issues or PRs
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Fixes #24538 

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

Make `PolyElement.as_expr()` accept symbols.

#### Release Notes

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  * Added a new solver for logarithmic equations.

* functions
  * Fixed a bug with log of integers.

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<!-- BEGIN RELEASE NOTES -->
* polys
  * Repaired a bug with `PolyElement.as_expr()`, so that it now accepts symbols.
<!-- END RELEASE NOTES -->

Update

The release notes on the wiki have been updated.

[github-actions]

Benchmark results from GitHub Actions

Lower numbers are good, higher numbers are bad. A ratio less than 1
means a speed up and greater than 1 means a slowdown. Green lines
beginning with + are slowdowns (the PR is slower then master or
master is slower than the previous release). Red lines beginning
with - are speedups.

Significantly changed benchmark results (PR vs master)

Significantly changed benchmark results (master vs previous release)

       before           after         ratio
     [41d90958]       [193e3825]
     <sympy-1.11.1^0>                 
-     1.22±0.05ms         746±20μs     0.61  solve.TimeSparseSystem.time_linear_eq_to_matrix(10)
-      3.42±0.1ms      1.42±0.07ms     0.41  solve.TimeSparseSystem.time_linear_eq_to_matrix(20)
-      6.98±0.2ms      2.02±0.06ms     0.29  solve.TimeSparseSystem.time_linear_eq_to_matrix(30)

Full benchmark results can be found as artifacts in GitHub Actions
(click on checks at the top of the PR).