Support change the default location of legend in sympy plot.

[cocolato]

References to other Issues or PRs

Feature support #24339.
Now we can use the legend_loc field to place the legend at the corresponding corner of the axes/figure.
We can refer to the specific enumeration values from matplotlib.legend.Legend.

Brief description of what is fixed or changed

from sympy.plotting import plot, textplot
from sympy import exp
from sympy.abc import x

p = plot(1/(1+exp(-x)), exp(-x)/(1+exp(-x))**2, (x, -10, 10), \
    show=False, legend=True)
p.save("./my/test1.png")
p = plot(1/(1+exp(-x)), exp(-x)/(1+exp(-x))**2, (x, -10, 10), \
    show=False, legend=True, legend_loc="lower left")
p.save("./my/test2.png")
p = plot(1/(1+exp(-x)), exp(-x)/(1+exp(-x))**2, (x, -10, 10), \
    show=False, legend=True, legend_loc="center")
p.save("./my/test3.png")

test1.png

test2.png

test3.png

Other comments

Release Notes

• plotting
  • Support change the default location of legend in sympy plot.

[sympy-bot]

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Here is what the release notes will look like:

• plotting
  • Support change the default location of legend in sympy plot. (#24429 by @cocolato)

This will be added to https://github.com/sympy/sympy/wiki/Release-Notes-for-1.13.

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#### References to other Issues or PRs
<!-- If this pull request fixes an issue, write "Fixes #NNNN" in that exact
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Feature support https://github.com/sympy/sympy/issues/24339.
Now we can use the legend_loc field to place the legend at the corresponding corner of the axes/figure.
We can refer to the specific enumeration values from [matplotlib.legend.Legend](https://matplotlib.org/stable/api/legend_api.html#module-matplotlib.legend).

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

```python
from sympy.plotting import plot, textplot
from sympy import exp
from sympy.abc import x

p = plot(1/(1+exp(-x)), exp(-x)/(1+exp(-x))**2, (x, -10, 10), \
    show=False, legend=True)
p.save("./my/test1.png")
p = plot(1/(1+exp(-x)), exp(-x)/(1+exp(-x))**2, (x, -10, 10), \
    show=False, legend=True, legend_loc="lower left")
p.save("./my/test2.png")
p = plot(1/(1+exp(-x)), exp(-x)/(1+exp(-x))**2, (x, -10, 10), \
    show=False, legend=True, legend_loc="center")
p.save("./my/test3.png")
```
test1.png
![image](https://user-images.githubusercontent.com/35182391/209567042-fc454c6e-1a6e-4cf6-a62c-47838be962ef.png)
test2.png
![image](https://user-images.githubusercontent.com/35182391/209567053-132547af-4250-4b7d-9691-30ab51fcee4f.png)
test3.png
![image](https://user-images.githubusercontent.com/35182391/209567073-030220ee-16f7-4acf-9fee-be74aef7316f.png)

#### Other comments


#### Release Notes

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  * Added a new solver for logarithmic equations.

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  * Fixed a bug with log of integers.

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<!-- BEGIN RELEASE NOTES -->
* plotting
  * Support change the default location of legend in sympy plot.
<!-- END RELEASE NOTES -->

[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]       [a44d1a27]
     <sympy-1.11.1^0>                 
-         952±2μs          624±2μs     0.66  solve.TimeSparseSystem.time_linear_eq_to_matrix(10)
-     2.74±0.01ms         1.17±0ms     0.43  solve.TimeSparseSystem.time_linear_eq_to_matrix(20)
-     5.49±0.04ms         1.72±0ms     0.31  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).

[cocolato]

Not sure why ci reported the error.