solve raises error on duplicate symbols

[smichr]

References to other Issues or PRs

Brief description of what is fixed or changed

Rather than deal in some unique way with a solve request that contains duplicate symbols, the presence of duplicates now raises an error. This seems like a good idea because there is no reason to include duplicates and it might indicate a typo of the person entering the request. Disallowing duplicates matches the behvior of nonlinsolve and linsolve

Other comments

There are lots of stray extra lines fixed in the first commit. Please review commits starting at 2 instead of looking at "Files changed" if that much noise is bothersome.

Release Notes

• solvers
  • solve now raises an error if duplicate symbols are given in the unknowns to be solved for such as solve(equations, [x, y, x]).

[sympy-bot]

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• solvers
  • solve now raises an error if duplicate symbols are given in the unknowns to be solved for such as solve(equations, [x, y, x]). (#23891 by @smichr)

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

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

Rather than deal in some unique way with a solve request that contains duplicate symbols, the presence of duplicates now raises an error. This seems like a good idea because there is no reason to include duplicates and it *might* indicate a typo of the person entering the request. Disallowing duplicates matches the behvior of `nonlinsolve` and `linsolve`

#### Other comments

There are lots of stray extra lines fixed in the first commit. Please review commits starting at 2 instead of looking at "Files changed" if that much noise is bothersome.

#### Release Notes

<!-- Write the release notes for this release below between the BEGIN and END
statements. The basic format is a bulleted list with the name of the subpackage
and the release note for this PR. For example:

* solvers
  * Added a new solver for logarithmic equations.

* functions
  * Fixed a bug with log of integers.

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<!-- BEGIN RELEASE NOTES -->
* solvers
  * `solve` now raises an error if duplicate symbols are given in the unknowns to be solved for such as `solve(equations, [x, y, x])`.
<!-- 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
     [ac3b08a6]       [3d85b8bd]
-     1.23±0.03ms         747±20μs     0.61  solve.TimeSparseSystem.time_linear_eq_to_matrix(10)
-     3.52±0.06ms      1.41±0.03ms     0.40  solve.TimeSparseSystem.time_linear_eq_to_matrix(20)
-     7.09±0.06ms      2.07±0.03ms     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).

[oscarbenjamin]

This doesn't catch the case of duplicated symbols when the input is not a list:

In [4]: solve(x, x, y, x)
Out[4]: [{x: 0}, {x: 0}]

In [5]: solve([x], x, y, x)
---------------------------------------------------------------------------
GeneratorsError

[smichr]

Thanks for the catch, @oscarbenjamin. This is ready to go.

[oscarbenjamin]

Looks good!