Got it. Thanks a lot. Best, Huq
On Mon, Sep 24, 2018 at 8:26 PM Matthew Knepley <[email protected]> wrote: > On Mon, Sep 24, 2018 at 9:02 PM Fazlul Huq <[email protected]> wrote: > >> Hello All, >> >> I am looking through the example problems given in PETSc. In the very >> first example, ex1 of vector section, I don't understand the following >> part, especially the term "PETSC_SMALL". What does this mean? >> > > This checks that we get the norm we expect. PETSC_SMALL is a small > difference we are willing to accept > due to roundoff error. > > Matt > > >> Here, in the second line we already assign zero to v. What is the meaning >> of "if" condition then? >> >> ierr = VecScale(x,two);CHKERRQ(ierr); >> ierr = VecNorm(x,NORM_2,&norm);CHKERRQ(ierr); >> v = norm-2.0*PetscSqrtReal((PetscReal)n); if (v > -PETSC_SMALL && v >> < PETSC_SMALL) v = 0.0; >> ierr = PetscPrintf(PETSC_COMM_WORLD,"VecScale >> %g\n",(double)v);CHKERRQ(ierr); >> >> >> All the best. >> Sincerely, >> Huq >> -- >> >> Fazlul Huq >> Graduate Research Assistant >> Department of Nuclear, Plasma & Radiological Engineering (NPRE) >> University of Illinois at Urbana-Champaign (UIUC) >> E-mail: [email protected] >> > > > -- > What most experimenters take for granted before they begin their > experiments is infinitely more interesting than any results to which their > experiments lead. > -- Norbert Wiener > > https://www.cse.buffalo.edu/~knepley/ > <http://www.cse.buffalo.edu/~knepley/> > -- Fazlul Huq Graduate Research Assistant Department of Nuclear, Plasma & Radiological Engineering (NPRE) University of Illinois at Urbana-Champaign (UIUC) E-mail: [email protected]
