[petsc-users] Question about DMDA local vector and global vector

[Danyang Su]

Hi Matthew,

How about the matview output? Is this automatically permuted to the 
natural ordering too?

Thanks,

Danyang

On 20/05/2014 12:25 PM, Matthew Knepley wrote:
> On Tue, May 20, 2014 at 1:31 PM, Danyang Su <danyang.su at gmail.com 
> <mailto:danyang.su at gmail.com>> wrote:
>
>     Hi All,
>
>     I use DMDA for a flow problem and found the local vector and
>     global vector does not match for 2D and 3D problem when dof >1.
>
>     For example, the mesh is as follows:
>
>     |proc 1|   proc 2 |   proc 3  |
>     |7  8  9|16 17 18|25 26 27|
>     |4  5  6|13 14 15|22 23 24|
>     |1  2  3|10 11 12|19 20 21|
>
>     /The following functions are used to create DMDA object, global
>     vector and local vector./
>
>     call DMDACreate2d(Petsc_Comm_World,DMDA_BOUNDARY_NONE, &
>                          DMDA_BOUNDARY_NONE,
>     DMDA_STENCIL_BOX,             &
>     nvxgbl,nvzgbl,PETSC_DECIDE,PETSC_DECIDE,          &
>                          dmda_flow%dof,
>     dmda_flow%swidth,                  &
>     PETSC_NULL_INTEGER,PETSC_NULL_INTEGER,            &
>                          dmda_flow%da,ierr)
>     call DMCreateGlobalVector(dmda_flow%da,x_flow,ierr)
>     call VecDuplicate(x_flow,b_flow,ierr)
>     call DMCreateLocalVector(dmda_flow%da,x_flow_loc,ierr)
>     call VecDuplicate(x_flow_loc,b_flow_loc,ierr)
>
>     /The following functions are used to compute the function
>     (b_flow_loc)/
>
>     call VecGetArrayF90(b_flow_loc, vecpointer, ierr)
>     vecpointer = (compute the values here...)
>     call VecRestoreArrayF90(b_flow_loc,vecpointer,ierr)
>     call DMLocalToGlobalBegin(dmda_flow%,b_flow_loc,INSERT_VALUES, &
>                               b_flow,ierr)
>     call DMLocalToGlobalEnd(dmda_flow%,b_flow_loc,INSERT_VALUES, &
>                               b_flow,ierr)
>
>
>     /The data of local vector b_flow_loc for proc1, proc2 and proc3
>     are as follows (just an example, without ghost value)/
>     proc 1  proc 2   proc 3
>       1        10        19
>       2        11        20
>       3        12        21
>       4        13        22
>       5        14        23
>       6        15        24
>       ...      ...       ...
>
>     /But the global vector b_flow from Vecview shows that the data is
>     stored as follows (left column). I thought the global vector
>     b_flow is like the right column. Is anything wrong here?/
>
>
> On output, the global vectors are automatically permuted to the 
> natural ordering.
>
>    Matt
>
>
>     Process [0]            Process [0]
>     1                              1
>     2                              2
>     3                              3
>     10                            4
>     11                            5
>     12                            6
>     ...                              ...
>     Process [1]            Process [1]
>     4                              10
>     5                              11
>     6                              12
>     13                            13
>     14                            14
>     15                            15
>     ...                              ...
>     Process [2]            Process [2]
>     ...                            ...
>
>     Though the data distribution is different from what I thought
>     before, the code works well for 1D problem and most of the 2D and
>     3D problem, but failed in newton iteration for some 2D problem
>     with dof > 1. I use KSP solver, not SNES solver at present.
>
>     Thanks and regards,
>
>     Danyang
>
>
>
>
>
> -- 
> 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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