dendrograms/astrodendro — pull request #125 by tomr-stargazer (2014-08-07 17:52:40+00:00)
Title: Asymmetry in periodic structure finding.

I noticed some funny behavior with computing periodic structures (partially noted in #123, which is a bit of a mess), and honed it down to this. `test_periodic_left` is failing for me while `test_periodic_right` passes.

```python
def test_periodic_left():
x = np.array([[1, 0, 0, 0, 0],
[1, 0, 0, 0, 1],
[1, 0, 0, 0, 0]])
d = Dendrogram.compute(x, min_value=0.5,
neighbours=periodic_neighbours(1))
expected = np.array([[0, -1, -1, -1, -1],
[0, -1, -1, -1, 0],
[0, -1, -1, -1, -1]])
np.testing.assert_array_equal(d.index_map, expected)
```

```python
E AssertionError:
E Arrays are not equal
E
E (mismatch 13.3333333333%)
E x: array([[ 0, -1, -1, -1, -1],
E [ 1, -1, -1, -1, 0],
E [ 2, -1, -1, -1, -1]], dtype=int32)
E y: array([[ 0, -1, -1, -1, -1],
E [ 0, -1, -1, -1, 0],
E [ 0, -1, -1, -1, -1]])
```

@ChrisBeaumont, do you have any insight as to why this might be the case? Perhaps some uncaught edge-case in `periodic_neighbours`? (also, sorry for the flurry of recent pull requests - I appreciate whatever time you've been able to devote to helping me out.)