8000 Improve test for MDS parallel processing case - requires update in MDS · Issue #10119 · scikit-learn/scikit-learn · GitHub
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Improve test for MDS parallel processing case - requires update in MDS #10119

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jsoutherland opened this issue Nov 13, 2017 · 2 comments
Open

Improve test for MDS parallel processing case - requires update in MDS #10119

jsoutherland opened this issue Nov 13, 2017 · 2 comments
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help wanted module:manifold module:test-suite everything related to our tests

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@jsoutherland
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Description

There is a test that MDS does not create an error when performing parallel processing (n_jobs > 1)
https://github.com/scikit-learn/scikit-learn/blob/master/sklearn/manifold/tests/test_mds.py#L55-L61

That test should also assert that the result is comparable to with n_jobs = 1.

Steps/Code to Reproduce

Proposed test:

def test_MDS_parallel():
    sim = np.array([[0, 5, 3, 4],
                    [5, 0, 2, 2],
                    [3, 2, 0, 1],
                    [4, 2, 1, 0]])
    mds_clf = mds.MDS(metric=False, n_jobs=1, n_init=4, dissimilarity="precomputed")
    result1 = mds_clf.fit(sim)

    # TODO: if sim is modified my MDS.fit then set it back before the next test

    mds_clf = mds.MDS(metric=False, n_jobs=4, n_init=4, dissimilarity="precomputed")
    result2 = mds_clf.fit(sim)

    assert_array_almost_equal(result1, result2, decimal=3)

... as a replacement for
https://github.com/scikit-learn/scikit-learn/blob/master/sklearn/manifold/tests/test_mds.py#L55-L61

The smacof algorithm involves an iterative search from n_init random initial solutions. In the parallel case each job searches from a new defined seed. In the non-parallel case, random_state is used to continue searching from a single starting seed. These varying approaches don't produce the same results. The non-parallel case must be modified to search from increasing seeds in order to be consistent with the parallel case. That will allow for consistent output when switching between the two parameter options and also allow for this new test to pass.

See
https://github.com/scikit-learn/scikit-learn/blob/master/sklearn/manifold/mds.py#L248-L271

Expected Results

Actual Results

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@anurag03
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@jsoutherland I want to work on this issue.

@jsoutherland
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@anurag03 go for it - thanks!

@jsoutherland jsoutherland mentioned this issue May 24, 2018
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@cmarmo cmarmo added module:manifold module:test-suite everything related to our tests labels Dec 23, 2021
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@jnothman @cmarmo @jsoutherland @anurag03
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