[petsc-users] inserting multiple rows together into a matrix

[Matthew Knepley]

On Wed, Apr 15, 2020 at 9:30 PM Bin Liu <lbllm2018 at hotmail.com> wrote:

> Sure. Thanks for your information.  Actually, I used to call MatSetValues
> for each column. Since my matrix is sparse and I am not sure whether the
> non-zeros along each column are identical for each row, I am currently
> wondering if it is possible to insert the entire local dense matrix into
> the global sparse matrix using a single MatSetValues routine. Would it be
> more efficient than I identify the nonzeros and inserting them row-by-row?
> I may also set the “IGNORE_ZERO_ENTRIES” for the global sparse matrix
> before “MatSetValues”. Would it be helpful?
>

Inserting a dense matrix is likely the wrong thing to do. Generally
row-by-row insertion is good.

  Thanks,

    Matt


> Thanks for your helps.
>
>
>
> *From:* Matthew Knepley [mailto:knepley at gmail.com]
> *Sent:* Wednesday, 15 April 2020 7:01 PM
> *To:* Bin Liu <lbllm2018 at hotmail.com>
> *Cc:* Junchao Zhang <junchao.zhang at gmail.com>; petsc-users at mcs.anl.gov
> *Subject:* Re: [petsc-users] inserting multiple rows together into a
> matrix
>
>
>
> On Wed, Apr 15, 2020 at 1:24 AM Bin Liu <lbllm2018 at hotmail.com> wrote:
>
> Thanks for your example. My problem is resolved. Meanwhile I am wondering,
> if it is possible to make this example more flexible. I mean what if the
> columns in each row are different? Is there any way to insert them all
> together?
>
>
>
> No. If the columns are different, you make a separate calls to
> MatSetValues().
>
>
>
>   Thanks,
>
>
>
>     Matt
>
>
>
>
>
> Regards
>
> Bin
>
>
>
> *From:* Junchao Zhang [mailto:junchao.zhang at gmail.com]
> *Sent:* Monday, 13 April 2020 11:33 PM
> *To:* Bin Liu <lbllm2018 at hotmail.com>
> *Cc:* petsc-users at mcs.anl.gov
> *Subject:* Re: [petsc-users] inserting multiple rows together into a
> matrix
>
>
>
> Add two rows 2 ,4,  and each row has three nonzeros at column 3, 7, 9
>
> m=2;
>
> n=3;
>
> idxm[] = {2, 4};
>
> idxn[] = {3, 7, 9};
>
> v[6]   = {0.1, 0.2, ....};
>
> MatSetValues(mat, m, idxm, n, idxn,v, INSERT_VALUES);
>
>
> --Junchao Zhang
>
>
>
>
>
> On Mon, Apr 13, 2020 at 9:59 AM Bin Liu <lbllm2018 at hotmail.com> wrote:
>
> Hi all,
>
>
>
> I know how to insert values in one row into the matrix via routine
> “MatSetValues”. I understand I logically should be able to insert multiple
> rows into the matrix with one call of “MatSetValues”. However, I am not
> sure how to do it. I searched in the PETSc mail list and did not find a
> relevant question answered before. Could anyone help me and give me a
> simple example code?
>
>
>
> Regards
>
> B.
>
>
>
>
> --
>
> 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
>
>
>
> https://www.cse.buffalo.edu/~knepley/
> <http://www.cse.buffalo.edu/~knepley/>
>


-- 
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

https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/>
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