# Note requirements for certain RowMatrix methods in docs

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#### Details

• Type: Documentation
• Status: Resolved
• Priority: Trivial
• Resolution: Fixed
• Affects Version/s: 1.3.0
• Fix Version/s:
• Component/s:
• Labels:
None
• Target Version/s:

#### Description

From mbofb's comment in PR https://github.com/apache/spark/pull/4680:

```The description of RowMatrix.computeSVD and mllib-dimensionality-reduction.html should be more precise/explicit regarding the m x n matrix. In the current description I would conclude that n refers to the rows. According to http://math.stackexchange.com/questions/191711/how-many-rows-and-columns-are-in-an-m-x-n-matrix this way of describing a matrix is only used in particular domains. I as a reader interested on applying SVD would rather prefer the more common m x n way of rows x columns (e.g. http://en.wikipedia.org/wiki/Matrix_%28mathematics%29 ) which is also used in http://en.wikipedia.org/wiki/Latent_semantic_analysis (and also within the ARPACK manual:
“
N Integer. (INPUT) - Dimension of the eigenproblem.
NEV Integer. (INPUT) - Number of eigenvalues of OP to be computed. 0 < NEV < N.
NCV Integer. (INPUT) - Number of columns of the matrix V (less than or equal to N).
“
).

description of RowMatrix.computeSVD and mllib-dimensionality-reduction.html:
"We assume n is smaller than m." Is this just a recommendation or a hard requirement. This condition seems not to be checked and causing an IllegalArgumentException – the processing finishes even though the vectors have a higher dimension than the number of vectors.

description of RowMatrix. computePrincipalComponents or RowMatrix in general:
I got a Exception.
java.lang.IllegalArgumentException: Argument with more than 65535 cols: 7949273
at org.apache.spark.mllib.linalg.distributed.RowMatrix.checkNumColumns(RowMatrix.scala:131)
at org.apache.spark.mllib.linalg.distributed.RowMatrix.computeCovariance(RowMatrix.scala:318)
at org.apache.spark.mllib.linalg.distributed.RowMatrix.computePrincipalComponents(RowMatrix.scala:373)
This 65535 cols restriction would be nice to be written in the doc (if this still applies in 1.3).
```

#### People

• Assignee:
Sean R. Owen
Reporter:
Xiangrui Meng
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#### Dates

• Created:
Updated:
Resolved: