Add Welford's online algorithm

[rlouf]

Closes #36.

[codecov]

Codecov Report

Merging #38 (a268c79) into main (9011be2) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##              main       #38   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           10        10           
  Lines          362       385   +23     
  Branches        14        17    +3     
=========================================
+ Hits           362       385   +23     

Impacted Files	Coverage Δ
aehmc/algorithms.py	100.00% <100.00%> (ø)

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[rlouf]

This is ready for review. The code will eventually go in aehmc/algorithms.py when #34 is merged.

[brandonwillard]

Looks great! Just a minor question/change regarding one of the function arguments.

[brandonwillard]

Should this really be called n_dims and should it be typed as TensorVariable, instead of—say—int? According to its use, it looks like it should be called "size" or "length".

In general, it isn't possible to have a symbolic/variable number of dimensions in most—if not all—tensor libraries, including Aesara.

[rlouf]

Replaced TensorVariable with int. The variable corresponds to the number of dimensions of the problem.

[rlouf]

I made the requested change, and rebased on main after having merged #35