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From Reza Zadeh <r...@databricks.com>
Subject Re: RowMatrix multiplication
Date Mon, 12 Jan 2015 18:58:48 GMT
As you mentioned, you can perform A * b, where A is a rowmatrix and b is a
local matrix.

>From your email, I figure you want to compute b * A^T. To do this, you can
compute C = A b^T, whose result is the transpose of what you were looking
for, i.e. C^T = b * A^T. To undo the transpose, you would have transpose C
manually yourself. Be careful though, because the result might not have
each Row fit in memory on a single machine, which is what RowMatrix
requires. This danger is why we didn't provide a transpose operation in
RowMatrix natively.

To address this and more, there is an effort to provide more comprehensive
linear algebra through block matrices, which will likely make it to 1.3:
https://issues.apache.org/jira/browse/SPARK-3434

Best,
Reza

On Mon, Jan 12, 2015 at 6:33 AM, Alex Minnaar <aminnaar@verticalscope.com>
wrote:

>  I have a rowMatrix on which I want to perform two multiplications.  The
> first is a right multiplication with a local matrix which is fine.  But
> after that I also wish to right multiply the transpose of my rowMatrix with
> a different local matrix.  I understand that there is no functionality to
> transpose a rowMatrix at this time but I was wondering if anyone could
> suggest a any kind of work-around for this.  I had thought that I might be
> able to initially create two rowMatrices - a normal version and a
> transposed version - and use either when appropriate.  Can anyone think of
> another alternative?
>
>
>  Thanks,
>
>
>  Alex
>

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