How to copy global data to local ?

[Barry Smith]

    You misunderstand the usage of MatGetSubMatrix(). Any process can  
request ANY row, including rows that are not originally owned by that  
process.

    Barry

On Dec 1, 2009, at 8:29 AM, ming zhu wrote:

> It seems that MatGetSubMatrix() only get the local matrix for the  
> processor  If U is global(PETSC_COMM_WORLD), the local matrix may  
> not store the column or row I wanted. For example, if U is 4*4, and  
> there are 4 processors, processors one has local matrix 2*2, but i  
> need the third row, Then,MatGetSubmatrix() may not work
>
> --- 09年12月1日，周二, Barry Smith <bsmith at mcs.anl.gov> 写 
> 道：
>
> 发件人: Barry Smith <bsmith at mcs.anl.gov>
> 主题: Re: How to copy global data to local ?
> 收件人: "PETSc users list" <petsc-users at mcs.anl.gov>
> 日期: 2009年12月1日,周二,下午10:23
>
>
> On Nov 30, 2009, at 11:21 PM, ming zhu wrote:
>
> > Hi
> > I have a huge matrix U for all processors (PETSC_COMM_WORLD). I  
> only want to copy only two rows (i,j) for each local processor. i,j  
> is different for each processor and not related to rank.  I was  
> trying to use a vector filter (like, 00000010000). However, if the  
> vector is PETSC_COMM_WORLD, it will be changed by different  
> processor. So, how to make it ?
>                                                                                                                                                                          ^ 
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>
>    I do not understand what this means. To do the multiply you can  
> and should use a vector of PETSC_COMM_WORLD.
>
>    Also multiplying by a vector will not give you back "rows" of a  
> matrix. Do you truly want the entire row of nonzeros of the matrix  
> or something else. If you want the entire row or part of a row then  
> you can use MatGetSubMatrix().
>
>    Barry
>
> > Thank you
> >
> > My original code is
> >
> > Vec filter
> > VecCreate(PETSC_COMM_WORLD,&filter);
> > VecSetsizes(filter,PETSC_DECIDE,m);
> > VecSetFromOptions(filter);
> >
> > Vecset(filter,0);
> > VecSetValue(filter,i,1,INSERT_VALUES);
> >
> > ...
> > MatMult(U, filter,ui);
> >
> > If I create filter with PETSC_COMM_SELF, it is impossible for U  
> and filter to multiply.
> >
> >
> >
> >
> >
> > 好玩贺卡等你发，邮箱贺卡全新上线！
>
>
> 好玩贺卡等你发，邮箱贺卡全新上线！