[petsc-users] Preallocation of sequential matrix

[Maahi Talukder]

Dear All,


I am trying to preallocate the no of nonzeros in my matrix using the
parameter 'nnz'. Here 'row' is the parameter 'nnz'. The part of the code
that does that is the following-

..........................................................................................................................................................................................
*Do j = 2,xmax-1*

*Do i = 2,ymax-1*

*a = (ymax-2)*(j-2)+i-1-1*

*If(j.eq.2 .and. i .ge. 3 .and. i .le. (ymax-2))then*
*row(a) = 6*

*else if (j.eq.(xmax-1) .and. i.ge.3 .and. i .le. (ymax-2)) then*
*row(a) = 6*

*else if(i.eq.2 .and. j.ge.3 .and. j.le.(xmax-2))then*
*row(a) = 6*

*else if(i.eq.(ymax-1) .and. j.ge.3 .and. j.le.(xmax-2)) then*
*row(a) = 6*

*else if(i.eq.2 .and. j.eq.2) then*
*row(a) = 4*

*else if (i.eq.2 .and. j .eq. (xmax-1)) then*
*row(a)= 4*

*else if (i.eq.(ymax-1) .and. j .eq. 2) then*
*row(a) = 4*

*else if (i .eq. (ymax-1) .and. j .eq. (xmax-1)) then*
*row(a) = 4*

*else*
*row(a) = 9*

*end if*


*end do *

*end do *


*call MatCreateSeqAIJ(PETSC_COMM_SELF,N,N,ze,row,Mp,ierr)*

.................................................................................................................................................................................................

But I get the following error message :

[0]PETSC ERROR: --------------------- Error Message
--------------------------------------------------------------
[0]PETSC ERROR: Argument out of range
[0]PETSC ERROR: New nonzero at (61,124) caused a malloc
Use MatSetOption(A, MAT_NEW_NONZERO_ALLOCATION_ERR, PETSC_FALSE) to turn
off this check
[0]PETSC ERROR: See http://www.mcs.anl.gov/petsc/documentation/faq.html for
trouble shooting.
[0]PETSC ERROR: Petsc Release Version 3.10.2, unknown
[0]PETSC ERROR: ./Test5 on a arch-opt named CB272PP-THINK1 by maahi Tue Apr
23 21:39:26 2019
[0]PETSC ERROR: Configure options --with-debugging=0
--download-fblaslapack=1 PETSC_ARCH=arch-opt
[0]PETSC ERROR: #1 MatSetValues_SeqAIJ() line 481 in
/home/maahi/petsc/src/mat/impls/aij/seq/aij.c
[0]PETSC ERROR: #2 MatSetValues() line 1349 in
/home/maahi/petsc/src/mat/interface/matrix.c
[0]PETSC ERROR: --------------------- Error Message
--------------------------------------------------------------
[0]PETSC ERROR: Argument out of range
[0]PETSC ERROR: New nonzero at (124,186) caused a malloc
Use MatSetOption(A, MAT_NEW_NONZERO_ALLOCATION_ERR, PETSC_FALSE) to turn
off this check
[0]PETSC ERROR: See http://www.mcs.anl.gov/petsc/documentation/faq.html for
trouble shooting.
[0]PETSC ERROR: Petsc Release Version 3.10.2, unknown
[0]PETSC ERROR: ./Test5 on a arch-opt named CB272PP-THINK1 by maahi Tue Apr
23 21:39:26 2019
[0]PETSC ERROR: Configure options --with-debugging=0
--download-fblaslapack=1 PETSC_ARCH=arch-opt
[0]PETSC ERROR: #3 MatSetValues_SeqAIJ() line 481 in
/home/maahi/petsc/src/mat/impls/aij/seq/aij.c
[0]PETSC ERROR: #4 MatSetValues() line 1349 in
/home/maahi/petsc/src/mat/interface/matrix.c
[0]PETSC ERROR: --------------------- Error Message
--------------------------------------------------------------
.................................................................................................................................................................................

But instead of using 'nnz', if I put a upper bound for 'nz',  the code
works fine.

Any idea what went wrong?

Thanks,
Maahi Talukder
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