Remove sparse option in Graph geometry

[michalk8]

closes #328

[codecov-commenter]

Codecov Report

Merging #329 (259d10e) into main (ce0301e) will decrease coverage by 0.07%.
The diff coverage is 97.14%.

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Additional details and impacted files

@@            Coverage Diff             @@
##             main     #329      +/-   ##
==========================================
- Coverage   88.65%   88.59%   -0.07%     
==========================================
  Files          52       51       -1     
  Lines        5668     5479     -189     
  Branches      864      824      -40     
==========================================
- Hits         5025     4854     -171     
+ Misses        518      509       -9     
+ Partials      125      116       -9     

Impacted Files	Coverage Δ
src/ott/geometry/graph.py	94.79% <97.14%> (+2.91%)	⬆️
src/ott/math/utils.py	85.71% <0.00%> (-8.17%)	⬇️

[marcocuturi]

thanks Michal, is there a reason (apart from the fact that it's not that clean) that we should remove this? any bugs this is causing?

[michalk8]

thanks Michal, is there a reason (apart from the fact that it's not that clean) that we should remove this? any bugs this is causing?

Yes, there are some bugs with the current sparse implementation sometimes not working (because of the factor cache).

[marcocuturi]

Ok LGTM then!