Add discrete convolution of two vectors

[Tobias271828]

This adds discrete convolutions.

A discrete convolution of two vectors [a1, a2, a3, ...] and [b1, b2, b3, ...] is the vector [a1*b1, a2*b1 + a1*b2, a3*b1 + a2*b2 + a1*b3, ...].

This function behaves similar to convolve in NumPy (Python).

This moves oscar-system/Oscar.jl#5997 to Nemo instead of Oscar. For more information concerning

• Different approaches to implementing this (naive approach, polynomial multiplication, pure pointwise multiplication of Fourier transformed vectors)
• Benchmarking comparisons of those
• Possible use cases of this

see oscar-system/Oscar.jl#5997

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.32%. Comparing base (0edb516) to head (36a90c4).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2299      +/-   ##
==========================================
- Coverage   88.35%   88.32%   -0.04%     
==========================================
  Files         102      102              
  Lines       37463    37468       +5     
==========================================
- Hits        33101    33093       -8     
- Misses       4362     4375      +13     

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[thofma]

Looks good. A small test would be nice. (Also the file needs to end with a newline.)