That's not quite what I'm looking for. Let me provide an example. I have a rowmatrix A that
is nxm and I have two local matrices b and c. b is mx1 and c is nx1. In my spark job I wish
to perform the following two computations
A*b
and
A^T*c
I don't think this is possible without being able to transpose a rowmatrix. Am I correct?
Thanks,
Alex
________________________________
From: Reza Zadeh <reza@databricks.com>
Sent: Monday, January 12, 2015 1:58 PM
To: Alex Minnaar
Cc: user@spark.incubator.apache.org
Subject: Re: RowMatrix multiplication
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/SPARK3434
Best,
Reza
On Mon, Jan 12, 2015 at 6:33 AM, Alex Minnaar <aminnaar@verticalscope.com<mailto: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 workaround 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
