[FLASH-USERS] [EXT] Re: Retrieving values in HYPRE matrix

[Eddie Hansen]

Hi Tony,

I'm not sure if you can retrieve all the box values in a stencil-wise
manner from gr_hypreMatA the way you're thinking. If my understanding is
correct, the SetBoxValues routine uses the stencil and the offsets like a
guide so that it knows which entries in gr_hypreMatA to set or add to. So
when you use GetBoxValues this way, you're assigning "combined" matrix
entries from gr_hypreMatA to test and you'll have repeated values based on
the stencil and offsets.

In other words, let's say you're in 2D and your stencil is 5 points in this
order: (i,j), (i-1,j), (i+1,j), (i,j-1), (i,j+1). The GetBoxValues routine
will set test from matrix A as follows:
test(1) = A(i,j)
test(2) = A(i-1,j)
test(3) = A(i+1,j)
test(4) = A(i,j-1)
test(5) = A(i,j+1)
test(6) = A(i,j+1)
test(7) = A(i-1,j+1)
test(8) = A(i+1,j+1)
test(9) = A(i,j)
test(10) = A(i,j+2)
etc., etc.

I've dealt with the HYPRE setup routines in FLASH a lot since I'm the one
primarily in charge of implementing new implicit diffusion solvers.
However, much of HYPRE itself is still a mystery to me, so I could still be
wrong about how the SetBoxValues and GetBoxValues routines are operating.

Alternatively, if you're just interested in looking at gr_hypreMatA, you
can use the subroutine HYPRE_SStructMatrixPrint(). There should be some
lines in Grid_advanceDiffusion.F90 that you can uncomment to do this. Then
you can use matlab or whatever program you prefer to look at the matrix.



On Thu, Feb 25, 2021 at 9:09 PM Akash Dhruv <akashdhruv at email.gwu.edu>
wrote:

> Hi Tony,
>
> Can you share a snippet of the output? Also, can you try getting the
> BoxValues after HYPRE_SStructMatrixAssemble is called?
>
> Akash
>
>
>
> On Feb 25, 2021, at 9:48 PM, Alberti, Anthony L <
> anthony.alberti at oregonstate.edu> wrote:
>
> Hi folks,
>
> I’m interested in retrieving the values written to the matrix for the
> system of equations built in
> source/Grid/GridSolvers/HYPRE/UG/gr_hypreCreateMatrix.F90. After BoxVal is
> filled and then assigned to gr_hypreMatA(via the call to
> HYPRE_SStructMatrixSetBoxValues) I’ve added a snippet of code that
> attempts to retrieve the values just written to gr_hypreMatA and writes
> to the screen a comparison of BoxVal and an array of reals called test –
> see the snippet below. However, when I run this the values for BoxVal and
> test are not even close. Does anyone have an idea on how to alter this
> snippet so test and BoxVal are the same?
>
> allocate(test(nentries*product(datasize(1:NDIM)))) !nentries * total
> number of grid cells per block )
> call HYPRE_SStructMatrixGetBoxValues(gr_hypreMatA, mypart,
> gr_hypreLower(lb,1:NDIM), &
>      gr_hypreUpper(lb,1:NDIM), var, nentries, stencil_indices(1:nentries),
> test(:), ierr)
> do i=1,nentries*product(datasize(1:NDIM))
>    WRITE(*,fmt='(I4.0, 6X, E15.9, 6X, E15.9)') i, BoxVal(i), test(i)
> end do
> call exit(0)
>
> Thanks in advance,
> Tony
>
>
>
> -----------------------------------------------------------
> Tony Alberti
> Postdoctoral Scholar
> School of Nuclear Science and Engineering
> https://ne.oregonstate.edu/tony-alberti
> <https://urldefense.proofpoint.com/v2/url?u=https-3A__ne.oregonstate.edu_tony-2Dalberti&d=DwMFaQ&c=kbmfwr1Yojg42sGEpaQh5ofMHBeTl9EI2eaqQZhHbOU&r=6F-TMED_bsUqKfX7XKE7kRK41M2Ogti8WJdx1GwNjkQ&m=viEEdaFV01zo9zrxAe3CDWtm6Kozcf5kb-Yoh2znXIA&s=aObgG-RLEKrNZ5hGr5VKNmbiTxeqGRkOBnGgU1QNERw&e=>
>
>
>

-- 
Eddie Hansen, PhD
Postdoctoral Associate
University of Rochester
607-341-6126 | Flash Center
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