Teuchos - Trilinos Tools Package Version of the Day
ParameterList/cxx_main.cpp

This is an example of how to use the Teuchos::ParameterList class.

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#include "Teuchos_ParameterList.hpp"
#include "Teuchos_StandardParameterEntryValidators.hpp"
#include "Teuchos_Array.hpp"  
#include "Teuchos_Version.hpp"
#include "Teuchos_as.hpp"

int main(int argc, char* argv[])
{

  using Teuchos::ParameterList;
  using Teuchos::RCP;
  using Teuchos::Array;
  using Teuchos::tuple;
  using Teuchos::as;

  std::cout << Teuchos::Teuchos_Version() << std::endl << std::endl;

  // Creating an empty parameter list looks like:
  ParameterList myPL;

  // Setting parameters in this list can be easily done:
  myPL.set("Max Iters", 1550, "Determines the maximum number of iterations in the solver");
  myPL.set("Tolerance", 1e-10, "The tolerance used for the convergence check");
  
  // For the "Solver" option, create a validator that will automatically
  // create documentation for this parameter but will also help in validation.
  RCP<Teuchos::StringToIntegralParameterEntryValidator<int> >
    solverValidator = Teuchos::rcp(
      new Teuchos::StringToIntegralParameterEntryValidator<int>(
        Teuchos::tuple<std::string>( "GMRES", "CG", "TFQMR" )
        ,"Solver"
        )
      );
  myPL.set(
    "Solver"
    ,"GMRES" // This will be validated by solverValidator right here!
    ,"The type of solver to use"
    ,solverValidator
    );

  /* The templated ``set'' method should cast the input {\it value} to the
     correct data type.  However, in the case where the compiler is not casting the input
     value to the expected data type, an explicit cast can be used with the ``set'' method:
  */
  myPL.set("Tolerance", as<float>(1e-10), "The tolerance used for the convergence check");

  /* Reference-counted pointers can also be passed through a ParameterList.
     To illustrate this we will use the Array class to create an array of 10 doubles
     representing an initial guess for a linear solver, whose memory is being managed by a 
     RCP.
   */
  
  myPL.set<Array<double> >("Initial Guess", tuple<double>( 10, 0.0 ),
    "The initial guess as a RCP to an array object.");

  /* A hierarchy of parameter lists can be constructed using {\tt ParameterList}.  This 
     means another parameter list is a valid {\it value} in any parameter list.  To create a sublist
     in a parameter list and obtain a reference to it:
  */
  ParameterList& Prec_List = myPL.sublist("Preconditioner", false, 
    "Sublist that defines the preconditioner.");

  // Now this parameter list can be filled with values:
  Prec_List.set("Type", "ILU", "The tpye of preconditioner to use");
  Prec_List.set("Drop Tolerance", 1e-3, 
    "The tolerance below which entries from the\n""factorization are left out of the factors.");

  // The parameter list can be queried about the existance of a parameter, sublist, or type:
  // Has a solver been chosen?
  bool solver_defined = false, prec_defined = false, dtol_double = false;
  solver_defined = myPL.isParameter("Solver");
  TEUCHOS_ASSERT_EQUALITY(solver_defined, true);  
  // Has a preconditioner been chosen?
  prec_defined = myPL.isSublist("Preconditioner"); 
  TEUCHOS_ASSERT_EQUALITY(prec_defined, true);  
  // Has a tolerance been chosen and is it a double-precision number?
  bool tol_double = false;
  tol_double = myPL.INVALID_TEMPLATE_QUALIFIER isType<double>("Tolerance");
  TEUCHOS_ASSERT_EQUALITY(tol_double, false); // It is 'float'!
  // Has a drop tolerance been chosen and is it a double-precision number?
  dtol_double = Teuchos::isParameterType<double>(Prec_List, "Drop Tolerance"); 
  TEUCHOS_ASSERT_EQUALITY(dtol_double, true);

  // Parameters can be retrieved from the parameter list in quite a few ways:
  // Get method that creates and sets the parameter if it doesn't exist.
  int its = -1;
  its = myPL.get("Max Iters", 1200);
  TEUCHOS_ASSERT_EQUALITY(its, 1550); // Was already ste
  // Get method that retrieves a parameter of a particular type that must exist.
  float tol = -1.0;
  tol = myPL.get<float>("Tolerance");
  TEUCHOS_ASSERT_EQUALITY(tol, as<float>(1e-10));
  // Get the "Solver" value and validate!
  std::string
    solver = solverValidator->validateString(
      Teuchos::getParameter<std::string>(myPL,"Solver")
      );

  // We can use this same syntax to get arrays out, like the initial guess.
  Array<double> init_guess = myPL.get<Array<double> >("Initial Guess");

  std::cout << "\n# Printing this parameter list using opeator<<(...) ...\n\n";
  std::cout << myPL << std::endl;

  std::cout << "\n# Printing the parameter list only showing documentation fields ...\n\n";
  myPL.print(std::cout,
    ParameterList::PrintOptions().showDoc(true).indent(2).showTypes(true)); 

  /* It is important to note that mispelled parameters 
     (with additional space characters, capitalizations, etc.) may be ignored.  
     Therefore, it is important to be aware that a given parameter has not been used. 
     Unused parameters can be printed with method:
  */ 
  std::cout << "\n# Showing unused parameters ...\n\n";
  myPL.unused( std::cout );

  return 0;

}
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