[petsc-users] PCDiagonalScale

[Barry Smith]

On Feb 23, 2011, at 9:45 AM, Klaij, Christiaan wrote:

> I'm trying to understand the use of PCDiagonalScale since I want to apply additional diagonal scaling when solving my linear system.

   Do you want to use it exactly for the reason given in 
   PCSetDiagonalScale - Indicates the left scaling to use to apply an additional left and right
      scaling as needed by certain time-stepping codes.

   Logically Collective on PC

   Input Parameters:
+  pc - the preconditioner context
-  s - scaling vector

   Level: intermediate

   Notes: The system solved via the Krylov method is
$           D M A D^{-1} y = D M b  for left preconditioning or
$           D A M D^{-1} z = D b for right preconditioning


> 
> As a first step I modified src/ksp/ksp/examples/tutorials/ex2f.F in petsc-3.1-p7 as follows:
> 
> 1) at line 87 added 3 lines:
>      PC          pc
>      PCType      ptype
>      PetscScalar tol
> 
> 2) then I uncommented lines 247 -- 252 (the ones to use PCJACOBI)
> 
> 3) at line 253 I added :
>      call PCDiagonalScale(pc,PETSC_TRUE,ierr)
> 
> Running "make ex2f" gives:
> 
> ex2f.o: In function `MAIN__':
> ex2f.F:(.text+0x767): undefined reference to `pcdiagonalscale_'
> 
> Without the call to PCDiagonalScale "make ex2f" does not give any errors and runs fine...
> 
> 
> dr. ir. Christiaan Klaij
> CFD Researcher
> Research & Development
> E mailto:C.Klaij at marin.nl
> T +31 317 49 33 44
> 
> MARIN
> 2, Haagsteeg, P.O. Box 28, 6700 AA Wageningen, The Netherlands
> T +31 317 49 39 11, F +31 317 49 32 45, I www.marin.nl
>