[petsc-users] Norm_2 calculation

[Fazlul Huq]

Hello All,
I'm trying to calculate the norm_2 error of a solution.
Here, vector s: Analytical solution
          vector x: Numerical solution

ierr = VecView(s,PETSC_VIEWER_STDOUT_WORLD);CHKERRQ(ierr);
ierr = VecView(x,PETSC_VIEWER_STDOUT_WORLD);CHKERRQ(ierr);

 ierr = VecAXPY(x,-1.0,s);CHKERRQ(ierr);
 ierr = VecNorm(x,NORM_2,&norm);CHKERRQ(ierr);
 ierr = VecView(x,PETSC_VIEWER_STDOUT_WORLD);CHKERRQ(ierr);
 ierr = KSPGetIterationNumber(ksp,&its);CHKERRQ(ierr);
 if (norm > tol) {
    ierr = PetscPrintf(PETSC_COMM_WORLD,"Second Norm of error %g\n",
double)norm);CHKERRQ(ierr);
    ierr = PetscPrintf(PETSC_COMM_WORLD,"Iterations
%D\n",its);CHKERRQ(ierr);
  }

Am I calculating the "Norm_2" error correctly or making any mistake?
Unfortunately, for large sized matrix, say 10^6, I am getting very high
value of "Norm_2" error.

Thank you.
Sincerely,
Huq

-- 

Fazlul Huq
Graduate Research Assistant
Department of Nuclear, Plasma & Radiological Engineering (NPRE)
University of Illinois at Urbana-Champaign (UIUC)
E-mail: huq2090 at gmail.com
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