compute the matrix of an isogeny on a given n-torsion subgroup

[yyyyx4]

Fixes #34879.

[codecov-commenter]

Codecov Report

Base: 88.57% // Head: 88.58% // Increases project coverage by +0.01% 🎉

Coverage data is based on head (58193bf) compared to base (52a81cb).
Patch coverage: 83.33% of modified lines in pull request are covered.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop   #35164      +/-   ##
===========================================
+ Coverage    88.57%   88.58%   +0.01%     
===========================================
  Files         2140     2140              
  Lines       397273   397297      +24     
===========================================
+ Hits        351891   351955      +64     
+ Misses       45382    45342      -40     

Impacted Files	Coverage Δ
src/sage/schemes/elliptic_curves/hom.py	83.33% <83.33%> (ø)
src/sage/groups/affine_gps/euclidean_group.py	88.88% <0.00%> (-11.12%)	⬇️
src/sage/homology/matrix_utils.py	84.40% <0.00%> (-3.67%)	⬇️
src/sage/groups/affine_gps/affine_group.py	96.62% <0.00%> (-2.25%)	⬇️
src/sage/modular/local_comp/liftings.py	98.33% <0.00%> (-1.67%)	⬇️
src/sage/combinat/combination.py	93.50% <0.00%> (-1.50%)	⬇️
src/sage/cpython/_py2_random.py	75.20% <0.00%> (-1.24%)	⬇️
...e/combinat/cluster_algebra_quiver/mutation_type.py	51.42% <0.00%> (-0.72%)	⬇️
src/sage/groups/generic.py	88.34% <0.00%> (-0.68%)	⬇️
src/sage/modular/modform/numerical.py	94.19% <0.00%> (-0.65%)	⬇️
... and 32 more

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[JohnCremona]

OK, I will review this

[github-actions]

Documentation preview for this PR is ready! 🎉
Built with commit: 58193bf