<p dir="auto">Per conversation in issue <a class="issue-link js-issue-link" data-error-text="Failed to load title" data-id="20774554" data-permission-text="Title is private" data-url="https://github.com/scikit-learn/scikit-learn/issues/2507" data-hovercard-type="issue" data-hovercard-url="/scikit-learn/scikit-learn/issues/2507/hovercard" href="https://github.com/scikit-learn/scikit-learn/issues/2507">#2507</a>, IsotonicRegression appears to have regressed due to commit <a class="commit-link" data-hovercard-type="commit" data-hovercard-url="https://github.com/scikit-learn/scikit-learn/commit/a9ea55fb404ba3a2411afa7a329f69eda67ca86c/hovercard" href="https://github.com/scikit-learn/scikit-learn/commit/a9ea55fb404ba3a2411afa7a329f69eda67ca86c"><tt>a9ea55f</tt></a>.</p>
<p dir="auto"><a href="http://nbviewer.ipython.org/urls/gist.githubusercontent.com/mjbommar/74fcefdcd0f2b1a5f708/raw/4742691db799101091598922cd0808f1eb5f07f2/isotonic_test_case_20150129.json" rel="nofollow">This IPython notebook</a> demonstrates the failure on HEAD.</p>
<p dir="auto">I tested the following two commits with the notebook:</p>
<ul dir="auto">
<li>
<p dir="auto"><a class="commit-link" data-hovercard-type="commit" data-hovercard-url="https://github.com/scikit-learn/scikit-learn/commit/d255866c667b74801b68e828b6fb5a769c531662/hovercard" href="https://github.com/scikit-learn/scikit-learn/commit/d255866c667b74801b68e828b6fb5a769c531662"><tt>d255866</tt></a>: no difference, SUCCESS</p>
</li>
<li>
<p dir="auto"><a class="commit-link" data-hovercard-type="commit" data-hovercard-url="https://github.com/scikit-learn/scikit-learn/commit/a9ea55fb404ba3a2411afa7a329f69eda67ca86c/hovercard" href="https://github.com/scikit-learn/scikit-learn/commit/a9ea55fb404ba3a2411afa7a329f69eda67ca86c"><tt>a9ea55f</tt></a>: difference, FAILURE</p>
<p dir="auto">In other words, I think we can blame the switch for <code class="notranslate">interp1d</code> from "linear" to "slinear"; first thought is that 1-d spline "slinear" matrix formulation is ill-posed for x-ties, whereas the piecewise "linear" implementation is unaffected?</p>
</li>
</ul>
<p dir="auto">Small additional note: confirmed failure with test case where x-values are all non-zero,  e.g., <code class="notranslate">[1, 1, 2, 3, 4]</code> instead of <code class="notranslate">[0, 0, 1, 2, 3]</code>, so <code class="notranslate">x=0</code> isn't part of the cause.</p>
<p dir="auto">Since we're now using upstream numpydoc, it should be fairly easy to fix the remaining errors in building the docs:</p>
<div class="snippet-clipboard-content notranslate position-relative overflow-auto" data-snippet-clipboard-copy-content="/home/ubuntu/scikit-learn/doc/modules/cross_validation.rst:287: WARNING: undefined label: time_series_cv (if the link has no caption the label must precede a section header)
/home/ubuntu/scikit-learn/doc/modules/cross_validation.rst:287: WARNING: undefined label: group_cv (if the link has no caption the label must precede a section header)
/home/ubuntu/scikit-learn/sklearn/covariance/outlier_detection.py:docstring of sklearn.covariance.EllipticEnvelope.correct_covariance:4: WARNING: citation not found: Rouseeuw1984
/home/ubuntu/scikit-learn/sklearn/covariance/outlier_detection.py:docstring of sklearn.covariance.EllipticEnvelope.reweight_covariance:4: WARNING: citation not found: Rouseeuw1984
/home/ubuntu/scikit-learn/sklearn/covariance/robust_covariance.py:docstring of sklearn.covariance.MinCovDet.correct_covariance:4: WARNING: citation not found: Rouseeuw1984
/home/ubuntu/scikit-learn/sklearn/covariance/robust_covariance.py:docstring of sklearn.covariance.MinCovDet.reweight_covariance:4: WARNING: citation not found: Rouseeuw1984
/home/ubuntu/scikit-learn/doc/modules/generated/sklearn.linear_model.RandomizedLasso.rst:17: WARNING: undefined label: randomized_l1 (if the link has no caption the label must precede a section header)
/home/ubuntu/scikit-learn/sklearn/linear_model/randomized_l1.py:docstring of sklearn.linear_model.RandomizedLasso:25: WARNING: undefined label: randomized_l1 (if the link has no caption the label must precede a section header)
/home/ubuntu/scikit-learn/sklearn/linear_model/randomized_l1.py:docstring of sklearn.linear_model.RandomizedLasso:153: WARNING: undefined label: sphx_glr_auto_examples_linear_model_plot_sparse_recovery.py (if the link has no caption the label must precede a section header)
/home/ubuntu/scikit-learn/doc/modules/generated/sklearn.linear_model.RandomizedLogisticRegression.rst:17: WARNING: undefined label: randomized_l1 (if the link has no caption the label must precede a section header)
/home/ubuntu/scikit-learn/sklearn/linear_model/randomized_l1.py:docstring of sklearn.linear_model.RandomizedLogisticRegression:27: WARNING: undefined label: randomized_l1 (if the link has no caption the label must precede a section header)
/home/ubuntu/scikit-learn/sklearn/linear_model/randomized_l1.py:docstring of sklearn.linear_model.RandomizedLogisticRegression:138: WARNING: undefined label: sphx_glr_auto_examples_linear_model_plot_sparse_recovery.py (if the link has no caption the label must precede a section header)
/home/ubuntu/scikit-learn/doc/modules/generated/sklearn.linear_model.lasso_stability_path.rst:11: WARNING: undefined label: randomized_l1 (if the link has no caption the label must precede a section header)
/home/ubuntu/scikit-learn/sklearn/utils/deprecation.py:docstring of sklearn.linear_model.lasso_stability_path:67: WARNING: undefined label: sphx_glr_auto_examples_linear_model_plot_sparse_recovery.py (if the link has no caption the label must precede a section header)
/home/ubuntu/scikit-learn/doc/modules/generated/sklearn.mixture.VBGMM.rst:22: WARNING: undefined label: vbgmm (if the link has no caption the label must precede a section header)
/home/ubuntu/scikit-learn/sklearn/model_selection/_search.py:docstring of sklearn.model_selection.GridSearchCV:46: WARNING: undefined label: multivalued_scorer_wrapping (if the link has no caption the label must precede a section header)
/home/ubuntu/scikit-learn/sklearn/model_selection/_search.py:docstring of sklearn.model_selection.RandomizedSearchCV:61: WARNING: undefined label: multivalued_scorer_wrapping (if the link has no caption the label must precede a section header)
/home/ubuntu/scikit-learn/sklearn/model_selection/_validation.py:docstring of sklearn.model_selection.cross_validate:42: WARNING: undefined label: multivalued_scorer_wrapping (if the link has no caption the label must precede a section header)
/home/ubuntu/scikit-learn/sklearn/model_selection/_validation.py:docstring of sklearn.model_selection.permutation_test_score:38: WARNING: undefined label: _scoring_parameter (if the link has no caption the label must precede a section header)
/home/ubuntu/scikit-learn/sklearn/model_selection/_validation.py:docstring of sklearn.model_selection.permutation_test_score:38: WARNING: undefined label: _scoring (if the link has no caption the label must precede a section header)
/home/ubuntu/scikit-learn/doc/modules/generated/sklearn.neighbors.LSHForest.rst:21: WARNING: undefined label: approximate_nearest_neighbors (if the link has no caption the label must precede a section header)
/home/ubuntu/scikit-learn/sklearn/neighbors/lof.py:docstring of sklearn.neighbors.LocalOutlierFactor:78: WARNING: undefined label: sklearn.metrics.pairwise.pairwise_distances (if the link has no caption the label must precede a section header)
/home/ubuntu/scikit-learn/doc/modules/grid_search.rst:87: WARNING: undefined label: sphx_glr_auto_examples_model_selection_plot_multi_metric_evaluation (if the link has no caption the label must precede a section header)
/home/ubuntu/scikit-learn/doc/modules/grid_search.rst:186: WARNING: undefined label: sphx_glr_auto_examples_model_selection_plot_multi_metric_evaluation (if the link has no caption the label must precede a section header)"><pre class="notranslate"><code class="notranslate">/home/ubuntu/scikit-learn/doc/modules/cross_validation.rst:287: WARNING: undefined label: time_series_cv (if the link has no caption the label must precede a section header)
/home/ubuntu/scikit-learn/doc/modules/cross_validation.rst:287: WARNING: undefined label: group_cv (if the link has no caption the label must precede a section header)
/home/ubuntu/scikit-learn/sklearn/covariance/outlier_detection.py:docstring of sklearn.covariance.EllipticEnvelope.correct_covariance:4: WARNING: citation not found: Rouseeuw1984
/home/ubuntu/scikit-learn/sklearn/covariance/outlier_detection.py:docstring of sklearn.covariance.EllipticEnvelope.reweight_covariance:4: WARNING: citation not found: Rouseeuw1984
/home/ubuntu/scikit-learn/sklearn/covariance/robust_covariance.py:docstring of sklearn.covariance.MinCovDet.correct_covariance:4: WARNING: citation not found: Rouseeuw1984
/home/ubuntu/scikit-learn/sklearn/covariance/robust_covariance.py:docstring of sklearn.covariance.MinCovDet.reweight_covariance:4: WARNING: citation not found: Rouseeuw1984
/home/ubuntu/scikit-learn/doc/modules/generated/sklearn.linear_model.RandomizedLasso.rst:17: WARNING: undefined label: randomized_l1 (if the link has no caption the label must precede a section header)
/home/ubuntu/scikit-learn/sklearn/linear_model/randomized_l1.py:docstring of sklearn.linear_model.RandomizedLasso:25: WARNING: undefined label: randomized_l1 (if the link has no caption the label must precede a section header)
/home/ubuntu/scikit-learn/sklearn/linear_model/randomized_l1.py:docstring of sklearn.linear_model.RandomizedLasso:153: WARNING: undefined label: sphx_glr_auto_examples_linear_model_plot_sparse_recovery.py (if the link has no caption the label must precede a section header)
/home/ubuntu/scikit-learn/doc/modules/generated/sklearn.linear_model.RandomizedLogisticRegression.rst:17: WARNING: undefined label: randomized_l1 (if the link has no caption the label must precede a section header)
/home/ubuntu/scikit-learn/sklearn/linear_model/randomized_l1.py:docstring of sklearn.linear_model.RandomizedLogisticRegression:27: WARNING: undefined label: randomized_l1 (if the link has no caption the label must precede a section header)
/home/ubuntu/scikit-learn/sklearn/linear_model/randomized_l1.py:docstring of sklearn.linear_model.RandomizedLogisticRegression:138: WARNING: undefined label: sphx_glr_auto_examples_linear_model_plot_sparse_recovery.py (if the link has no caption the label must precede a section header)
/home/ubuntu/scikit-learn/doc/modules/generated/sklearn.linear_model.lasso_stability_path.rst:11: WARNING: undefined label: randomized_l1 (if the link has no caption the label must precede a section header)
/home/ubuntu/scikit-learn/sklearn/utils/deprecation.py:docstring of sklearn.linear_model.lasso_stability_path:67: WARNING: undefined label: sphx_glr_auto_examples_linear_model_plot_sparse_recovery.py (if the link has no caption the label must precede a section header)
/home/ubuntu/scikit-learn/doc/modules/generated/sklearn.mixture.VBGMM.rst:22: WARNING: undefined label: vbgmm (if the link has no caption the label must precede a section header)
/home/ubuntu/scikit-learn/sklearn/model_selection/_search.py:docstring of sklearn.model_selection.GridSearchCV:46: WARNING: undefined label: multivalued_scorer_wrapping (if the link has no caption the label must precede a section header)
/home/ubuntu/scikit-learn/sklearn/model_selection/_search.py:docstring of sklearn.model_selection.RandomizedSearchCV:61: WARNING: undefined label: multivalued_scorer_wrapping (if the link has no caption the label must precede a section header)
/home/ubuntu/scikit-learn/sklearn/model_selection/_validation.py:docstring of sklearn.model_selection.cross_validate:42: WARNING: undefined label: multivalued_scorer_wrapping (if the link has no caption the label must precede a section header)
/home/ubuntu/scikit-learn/sklearn/model_selection/_validation.py:docstring of sklearn.model_selection.permutation_test_score:38: WARNING: undefined label: _scoring_parameter (if the link has no caption the label must precede a section header)
/home/ubuntu/scikit-learn/sklearn/model_selection/_validation.py:docstring of sklearn.model_selection.permutation_test_score:38: WARNING: undefined label: _scoring (if the link has no caption the label must precede a section header)
/home/ubuntu/scikit-learn/doc/modules/generated/sklearn.neighbors.LSHForest.rst:21: WARNING: undefined label: approximate_nearest_neighbors (if the link has no caption the label must precede a section header)
/home/ubuntu/scikit-learn/sklearn/neighbors/lof.py:docstring of sklearn.neighbors.LocalOutlierFactor:78: WARNING: undefined label: sklearn.metrics.pairwise.pairwise_distances (if the link has no caption the label must precede a section header)
/home/ubuntu/scikit-learn/doc/modules/grid_search.rst:87: WARNING: undefined label: sphx_glr_auto_examples_model_selection_plot_multi_metric_evaluation (if the link has no caption the label must precede a section header)
/home/ubuntu/scikit-learn/doc/modules/grid_search.rst:186: WARNING: undefined label: sphx_glr_auto_examples_model_selection_plot_multi_metric_evaluation (if the link has no caption the label must precede a section header)
</code></pre></div>