[petsc-users] VecStrideScatter question

[Barry Smith]

On May 15, 2013, at 10:26 AM, Tabrez Ali <stali at geology.wisc.edu> wrote:

> The error message (with stride of 2) is
> 
> [1]PETSC ERROR: --------------------- Error Message ------------------------------------
> [1]PETSC ERROR: Argument out of range!
> [1]PETSC ERROR: Start of stride subvector (2) is too large for stride
> Have you set the vector blocksize (1) correctly with VecSetBlockSize()?!
> [1]PETSC ERROR: ------------------------------------------------------------------------
> 
> Do I have to use VecSetBlockSize as done in http://www.mcs.anl.gov/petsc/petsc-current/src/vec/vec/examples/tutorials/ex12.c.html
> 
> Actually my V1 (12 entries) and V2 (3 entries) are like
> 
> V1=[u1 v1 w1 u2 v2 w2 u3 v3 w3 a b c]' and
> 
> V2=[      x1       x2       x3      ]' what I eventually want is
> 
> V1=[u1 v1 w1+x1 u2 v2 w2+x2 u3 v3 w3+x3 a b c]
> 
> Would the [a b c] at the end of V1 cause problems?

   Yes, you'd need to have an extra entry at the end of V2 that contained a zero.

   Barry

> 
> Tabrez
> 
> 
> On 05/15/2013 09:46 AM, Jed Brown wrote:
>> Tabrez Ali<stali at geology.wisc.edu>  writes:
>> 
>>> Hello
>>> 
>>> I have two parallel vectors (same layout) of different lengths, e.g.,
>>> 
>>> V1=[u1 v1 w1 u2 v2 w2 u3 v3 w3]' and
>>> V2=[x1 x2 x3]'
>>> 
>>> and I wish to add them in a way such that
>>> 
>>> V3=[
>>> u1
>>> v1
>>> w1+x1
>>> u2
>>> v2
>>> w2+x2
>>> u3
>>> v3
>>> w3+x3
>>> ]
>>> 
>>> Is VecStrideScatter appropriate for this? I tried
>>> 
>>> call VecStrideScatter(V2,3,V1,Add_Values,ierr)
>>> 
>>> but it seems to fail.
>> "seems to fail" is not helpful, but in any case, the indexing starts at
>> 0 (so pass 2 instead of 3).
> 
> 
> -- 
> No one trusts a model except the one who wrote it; Everyone trusts an observation except the one who made it- Harlow Shapley
>