14.1. Runtime Options

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Allowing the user to modify parameters and options easily at runtime is very desirable for many applications. PETSc 2.0 provides a simple mechanism to enable such customization. To print a list of available options for a given program, simply specify the option -help (or -h) at runtime, e.g.,

    mpirun -np 1 ex1 -help 
Note that all runtime options correspond to particular PETSc routines that can be explicitly called from within a program to set compile-time defaults. For many applications it is natural to use a combination of compile-time and runtime choices. For example, when solving a linear system, one could explicitly specify use of the Krylov subspace technique BiCGStab by calling
    ierr = KSPSetType(ksp,KSPBCGS); 
One could then override this choice at runtime with the option
    -ksp_type tfqmr 
to select the Transpose-Free QMR algorithm. (See Chapter SLES: Linear Equations Solvers for details.)

The remainder of this section discusses details of runtime options.


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