Implement log-probability for CumSum Op

[ricardoV94]

import aesara.tensor as at
from aeppl import joint_logprob

rv = at.random.normal(0, 1, size=5).cumsum()
vv = rv.clone()

logp = joint_logprob({rv: vv}, sum=False)
logp.eval({vv: np.arange(1, 6)})
# array([-1.41893853, -1.41893853, -1.41893853, -1.41893853, -1.41893853])

[codecov]

Codecov Report

Merging #72 (ad37be1) into main (9298dac) will increase coverage by 0.13%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main      #72      +/-   ##
==========================================
+ Coverage   94.78%   94.92%   +0.13%     
==========================================
  Files           8        9       +1     
  Lines        1227     1260      +33     
  Branches      163      164       +1     
==========================================
+ Hits         1163     1196      +33     
  Misses         31       31              
  Partials       33       33              

Impacted Files	Coverage Δ
aeppl/cumsum.py	100.00% <100.00%> (ø)

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[brandonwillard]

Looks good, but I don't think the CumSum code should be in scan.py—that module is pretty specific to Scan.

In general, given the extent to which we're likely to expand Aesara Op coverage (i.e. a large extent), we should start creating new modules. For example, we could start mirroring the modules in which the Aesara Ops are defined—at least when we plan on having log-probability implementations for more than one Op from the same Aesara modules.

[ricardoV94]

Looks good, but I don't think the CumSum code should be in scan.py—that module is pretty specific to Scan.

Yeah, I was not very happy with it tucked in there either. Aesara puts this is extra_ops though, should we do the same or something more direct?

Edit: Otherwise, we can organize by conceptual types of RVs... like the mixtures. In that case there was a slight link between this and the scan rewrites

[brandonwillard]

Yeah, I was not very happy with it tucked in there either. Aesara puts this is extra_ops though, should we do the same or something more direct?

An extra_ops module is fine for now.

Edit: Otherwise, we can organize by conceptual types of RVs... like the mixtures.

Exactly

[brandonwillard]

Looks great!