pymc-devs / pymc-devs/pytensor
Rewrite to remove useless transpose followed by reduction
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graph rewriting
- Dominant language
- Python
- Stars
- 644
- Forks
- 208
- Avg merge
- 2d 14h
- Merged PRs (30d)
- 16
Description
Description
import pytensor
import pytensor.tensor as pt
x = pt.matrix("x")
y = pt.sum(x.T)
fn = pytensor.function([x], y)
fn.dprint()
Sum{axes=None} [id A] 1
└─ Transpose{axes=[1, 0]} [id B] 'x.T' 0
└─ x [id C]
If we can remove a transpose (dimshuffle) without affecting the output (sometimes by changing the reduction axes, sometimes without having to do anything), we could rewrite it away. That allows more succinct graphs and more extensive canonicalizaiton
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by reproducing the Python example with pt.sum(x.T) and inspecting its printed graph. Trace the graph-rewrite or optimization entry point that handles reductions and transposes, then verify that the transpose is absent while the result remains equivalent for the relevant axes.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python
- Domain
- backend
- Issue type
- Refactor
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 45/100