[petsc-users] Advice on how to tackle with in place operation for a Matrix

[Barry Smith]

  If you do want to do this with a dense matrix then just use MatGetArray() to directly access the matrix entries. Then you can skip the MatGetColumn() and MatSetValues() stuff.
But I agree with Matt that generally if you are doing orthogonalization it is a set of vectors you are doing it to. You then decide if you want to represent that collection of vectors as a dense matrix (which is the Matlab way) or as an array of vectors.

    Barry

On May 18, 2010, at 4:08 AM, Matthew Knepley wrote:

> On Tue, May 18, 2010 at 3:58 AM, Umut Tabak <u.tabak at tudelft.nl> wrote:
> Matthew Knepley wrote:
> 1) This must be a dense matrix, so you could directly copy in the values with a strided loop
> 
> Dear Matt,
> Thanks for the immediate reply, I guess I did not understand this.
> 
> 2) Is there a reason for the output to be a matrix, rather than a collection of vectors?
> 
> Collection of vectors? not sure on this point. After the orthogonalization, I extract some parts of the matrix and continue operation with these extracted parts. Are there better ways of conducting operations for these kinds of tasks?
> 
> Well, you generally do not want the parallel organization of a MPIDENSE when you make
> these sorts of updates. You want to access 1 column at a time, with the layout of a vector.
> Thus is generally makes more sense to me to use a Vec[] than a MPIDENSE.
> 
>     Matt
> 
> -- 
> What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead.
> -- Norbert Wiener

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