[ENH] Asymmetric peak_directions

[CHrlS98]

Hello,

Add a is_symmetric flag to dipy.direction.peaks.peak_directions to enable peak extraction on asymmetric ODFs. is_symmetric is True by default, so that the default behaviour does not change. When set to False, the sphere directions v and -v are considered distinct, such that it is possible to find a maxima along v but not along -v.

I simply removed the absolute value in remove_similar_vertices so that opposite sphere directions are not considered close to each other.

Have a good one!

[codecov]

Codecov Report

Merging #2751 (c877b96) into master (3667150) will increase coverage by 0.00%.
The diff coverage is n/a.

❗ Current head c877b96 differs from pull request most recent head 77fc969. Consider uploading reports for the commit 77fc969 to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2751   +/-   ##
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  Coverage   83.90%   83.90%           
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  Files         132      132           
  Lines       18468    18471    +3     
  Branches     3018     3017    -1     
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+ Hits        15496    15499    +3     
  Misses       2227     2227           
  Partials      745      745           

Impacted Files	Coverage Δ
dipy/direction/peaks.py	84.50% <ø> (ø)

... and 1 file with indirect coverage changes

[gabknight]

Thanks @CHrlS98. Looks good to me. Just a few minor suggestions.

[skoudoro]

Apart from the small comment below, all good to me.

Does someone else want to look at it before merging ???

[skoudoro]

Thanks @CHrlS98, merging!