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https://issues.apache.org/jira/browse/SPARK-12372?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Hyukjin Kwon resolved SPARK-12372.
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Resolution: Incomplete
> Document limitations of MLlib local linear algebra
> --------------------------------------------------
>
> Key: SPARK-12372
> URL: https://issues.apache.org/jira/browse/SPARK-12372
> Project: Spark
> Issue Type: Documentation
> Components: Documentation, MLlib
> Affects Versions: 1.5.2
> Reporter: Christos Iraklis Tsatsoulis
> Priority: Major
> Labels: bulk-closed
>
> This JIRA is now for documenting limitations of MLlib's local linear algebra
> types. Basically, we should make it clear in the user guide that they
> provide simple functionality but are not a full-fledged local linear library.
> We should also recommend libraries for users to use in the meantime:
> probably Breeze for Scala (and Java?) and numpy/scipy for Python.
> *Original JIRA title*: Unary operator "-" fails for MLlib vectors
> *Original JIRA text, as an example of the need for better docs*:
> Consider the following snippet in pyspark 1.5.2:
> {code:none}
> >>> from pyspark.mllib.linalg import Vectors
> >>> x = Vectors.dense([0.0, 1.0, 0.0, 7.0, 0.0])
> >>> x
> DenseVector([0.0, 1.0, 0.0, 7.0, 0.0])
> >>> -x
> Traceback (most recent call last):
> File "<stdin>", line 1, in <module>
> TypeError: func() takes exactly 2 arguments (1 given)
> >>> y = Vectors.dense([2.0, 0.0, 3.0, 4.0, 5.0])
> >>> y
> DenseVector([2.0, 0.0, 3.0, 4.0, 5.0])
> >>> x-y
> DenseVector([-2.0, 1.0, -3.0, 3.0, -5.0])
> >>> -y+x
> Traceback (most recent call last):
> File "<stdin>", line 1, in <module>
> TypeError: func() takes exactly 2 arguments (1 given)
> >>> -1*x
> DenseVector([-0.0, -1.0, -0.0, -7.0, -0.0])
> {code}
> Clearly, the unary operator {{-}} (minus) for vectors fails, giving errors
> for expressions like {{-x}} and {{-y+x}}, despite the fact that {{x-y}}
> behaves as expected.
> The last operation, {{-1*x}}, although mathematically "correct", includes
> minus signs for the zero entries, which again is normally not expected.
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