# [petsc-users] Transpose of Block Matrix with aij type

Karl Rupp rupp at mcs.anl.gov
Tue Apr 23 20:39:56 CDT 2013

```Hi Joon,

sorry, that was a pretty bad idea (wouldn't even work with square
matrices in general)

I'm afraid you'll have to set up new matrices A, B with the respective
entries. For performance reasons you better use a dense format since

Best regards,
Karli

On 04/23/2013 06:05 PM, Choi240 wrote:
> Hi,
>
> Thank you for your reply. But A1,A2 are not square(3x4). B1~B4 are 3x3
> matrices. So A1*B1 is not impossible.
>
> Best regards,
> Joon
>
>
>
>
> -------- Original message --------
> Subject: Re: [petsc-users] Transpose of Block Matrix with aij type
> From: Karl Rupp <rupp at mcs.anl.gov>
> To: Choi240 <choi240 at purdue.edu>
> CC: petsc-users at mcs.anl.gov
>
>
> Hi again,
>
> if you have control over the structure of B, what about computing
> [A1 A2] * [B1 B3; B2 B4]
>
> Best regards,
> Karli
>
>
> On 04/23/2013 05:17 PM, Choi240 wrote:
>  > Hi,
>  >
>  > I have to compute multiplication between two block matrices. It should
>  > be as follows:
>  >
>  > B1 | B2         A1        B1A1+B2A2
>  > ----------   *   ---   =   ---------------
>  > B3 | B4         A2        B3A1+B4A2
>  >
>  > However, I just have A =  [A1 A2]. So, I need to get A^T. Is there a way
>  > I can get the transpose of this block matrix with the MatTranspose()? Or
>  > do I have to use another function such as MatGetSubMatrices()?
>  >
>  > Thank you,
>  > Joon
>  >
>  >
>  >
>  > -------- Original message --------
>  > Subject: Re: [petsc-users] Transpose of Block Matrix with aij type
>  > From: Karl Rupp <rupp at mcs.anl.gov>
>  > To: petsc-users at mcs.anl.gov
>  > CC: choi240 at purdue.edu
>  >
>  >
>  > Hi,
>  >
>  > why would you expect that the transpose of a 3x8 matrix is not a
> 8x3-matrix?
>  >
>  > Best regards,
>  > Karli
>  >
>  >
>  > On 04/23/2013 03:27 PM, Joon hee Choi wrote:
>  >  > Hello,
>  >  >
>  >  > I tried to get transpose of block matrix(just with aij type), but the
>  > result was not a block matrix. For example,
>  >  >
>  >  > A =
>  >  > 1 2 3 4 | 4 3 2 1
>  >  > 2 3 4 5 | 5 4 3 2
>  >  > 3 4 5 6 | 6 5 4 3
>  >  >
>  >  >
>  >  > AT(expected) =
>  >  > 1 2 3 4
>  >  > 2 3 4 5
>  >  > 3 4 5 6
>  >  > -------
>  >  > 4 3 2 1
>  >  > 5 4 3 2
>  >  > 6 5 4 3
>  >  >
>  >  >
>  >  > AT(result) =
>  >  > 1 2 3
>  >  > 2 3 4
>  >  > 3 4 5
>  >  > 4 5 6
>  >  > 4 5 6
>  >  > 3 4 5
>  >  > 2 3 4
>  >  > 1 2 3
>  >  >