FIX: Division by 0 in scil_dti_metrics

[AntoineTheb]

Quick description

Closes #884.

Type of change

Check the relevant options.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Provide data, screenshots, command line to test (if relevant)

See tests

Checklist

• My code follows the style guidelines of this project (run autopep8)
• I added relevant citations to scripts, modules and functions docstrings and descriptions
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I moved all functions from the script file (except the argparser and main) to scilpy modules
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[karanphil]

Looks good! I'd be curious to know why the residuals are computed slice by slice as @AntoineTheb said. Maybe @mdesco or @arnaudbore or @frheault know?

[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 69.45%. Comparing base (5bcfd7f) to head (355eca5).
Report is 18 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1089      +/-   ##
==========================================
- Coverage   69.45%   69.45%   -0.01%     
==========================================
  Files         447      447              
  Lines       24025    24053      +28     
  Branches     3280     3291      +11     
==========================================
+ Hits        16687    16706      +19     
- Misses       5943     5949       +6     
- Partials     1395     1398       +3     

Components	Coverage Δ
Scripts	70.24% <75.00%> (-0.02%)	⬇️
Library	68.39% <ø> (+0.01%)	⬆️

[AntoineTheb]

Looks good! I'd be curious to know why the residuals are computed slice by slice as @AntoineTheb said. Maybe @mdesco or @arnaudbore or @frheault know?

I'm fairly sure it is done to reduce memory consumption. We could spend a few hours preemtively optimizing it by chunking the volume and multiprocessing but I don't think this is necessary right now @arnaudbore .