solveset with piecewise: issue 19718

[maurogaravello]

References to other Issues or PRs

Fixes #19718

Brief description of what is fixed or changed

Solveset with inequality and Piecewise does not work properly.
Indeed it is _solveset which returns a wrong result when an argument is a BooleanTrue.
Now, when the argument is a BooleanTrue, it returns the domain.

A test is added.

Other comments

Release Notes

• solvers
  • Handling of inequalities involving Piecewise is improved in solveset.

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• solvers
  • Handling of inequalities involving Piecewise is improved in solveset. (#19986 by @maurogaravello)

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#### References to other Issues or PRs
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Fixes #19718 


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

`Solveset` with `inequality` and `Piecewise` does not work properly.
Indeed it is `_solveset` which returns a wrong result when an argument is a `BooleanTrue`.
Now, when the argument is a `BooleanTrue`, it returns the domain.

A test is added.

#### Other comments


#### Release Notes

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on how to write release notes. The bot will check your release notes
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<!-- BEGIN RELEASE NOTES -->

- solvers
  - Handling of inequalities involving Piecewise is improved in solveset.

<!-- END RELEASE NOTES -->

Update

The release notes on the wiki have been updated.

[codecov]

Codecov Report

Merging #19986 into master will increase coverage by 0.057%.
The diff coverage is 100.000%.

@@              Coverage Diff              @@
##            master    #19986       +/-   ##
=============================================
+ Coverage   75.825%   75.882%   +0.057%     
=============================================
  Files          669       669               
  Lines       173475    173566       +91     
  Branches     40911     40970       +59     
=============================================
+ Hits        131539    131707      +168     
+ Misses       36210     36130       -80     
- Partials      5726      5729        +3     

[czgdp1807]

This line isn't covered by the tests according to this report. Can you please add some tests covering this line?

[maurogaravello]

Do you mean something like this?

    f = BooleanTrue()
    assert solveset(f, x, domain=Interval(-3, 10)) == Interval(-3, 10)

[czgdp1807]

Yes. This should work.

[czgdp1807]

@smichr Is this good to go?

[oscarbenjamin]

Looks good. Thanks!