Bug#1070201: Perhaps alignment-related?

[Gard Spreemann]

It seems that any `Tree` attribute that uses `self._get_node_ndarray()`
to get a *floating point* ndarray suffers from this weird behavior when
negating. Examples include `weighted_n_node_samples` and
`threshold`. However, attributes that use the same function to get
*integer* ndarrays don't. Examples include `n_node_samples` and
`feature`.

Moreover, *only negation* seems to be problematic. Multiplying by `-1.0` seems fine:

> (Pdb) clf.tree_.impurity.__neg__()
> array([-4.69135802e-001, -1.59149684e-314, -1.50000000e+000,       -2.12199579e-314,              nan])
> (Pdb) clf.tree_.impurity.__mul__(-1.0)
> array([-0.4691358 , -0.        , -0.22222222, -0.        , -0.])

Some further observations:

* On i386:
  (Pdb) clf.tree_.impurity.__array_interface__
  {'data': (161778564, False), 'strides': (44,), 'descr': [('', '<f8')], 'typestr': '<f8', 'shape': (5,), 'version': 3}

* On amd64:
  (Pdb) clf.tree_.impurity.__array_interface__
  {'data': (54432144, False), 'strides': (64,), 'descr': [('', '<f8')], 'typestr': '<f8', 'shape': (5,), 'version': 3}
  
* Note that 161778564 (the i386 data pointer) is not divisible by 8,
  while 54432144 (the amd64 data pointer) is.

* CI started failing between NumPy 1.24 and 1.26.

* Between NumPy 1.24 and 1.26, there seems to have been some work on
  SIMD-ifying array negation [1].

I haven't been able to dig deeper, but does this perhaps smell of an
alignment issue?


[1] https://github.com/numpy/numpy/commit/490b1e45ce16ca91d1c6a1e644f844179b5410eb
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 857 bytes
Desc: not available
URL: <http://alioth-lists.debian.net/pipermail/debian-science-maintainers/attachments/20240607/3d9583a0/attachment.sig>