Use of the command line options database

  Various settings in ParPre (and in fact in the underlying Petsc library) can be set by a function call in the program, eg PCSetType(the_pc,PCNONE);, or by using command line options.

Command line options can be set in any of the following ways:

• really on the command line:

  mpirun a.out -pc_type none
  

• by setting the options, in the environment variable PETSC_OPTIONS or in the .petscrc file or any other file which can then be passed through PetscInitialize;
• in the code:

      OptionsSetValue("-pc_type","ilu");
  

Sometimes command line options are formed from the basic options, eg to set the preconditioner type for subdomain solvers we use an option -sub_pc_type none.

See the Petsc manual for more information about setting options.