Yes you are correct, to do it with existing operations you would need a transpose on rowmatrix.
However, you can fairly easily perform the operation manually by doing a join (if the c vector is an RDD) or broadcasting c (if the c vector is small enough to fit in memory on a single machine). On Mon, Jan 12, 2015 at 11:45 AM, Alex Minnaar <aminn...@verticalscope.com> wrote: > 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 <r...@databricks.com> > *Sent:* Monday, January 12, 2015 1:58 PM > *To:* Alex Minnaar > *Cc:* u...@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/SPARK-3434 > > Best, > Reza > > On Mon, Jan 12, 2015 at 6:33 AM, Alex Minnaar <aminn...@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 >> > >
