Reorder the declaration of member variables.

This allows a significant simplification of the code flow in the
constructor.

diff --git a/examples/step-17/step-17.cc b/examples/step-17/step-17.cc
index 70f148db498e7401529985358be09a9525819698..f953b39f519e261b05b27c37e64668f5990a35f1 100644 (file)
--- a/examples/step-17/step-17.cc
+++ b/examples/step-17/step-17.cc
@@ -116,8 +116,27 @@ namespace Step17
     void refine_grid ();
     void output_results (const unsigned int cycle) const;
 
-    // The first difference to step-8 is the introduction of a
-    // stream-like variable <code>pcout</code>. It is, in essence,
+    // The first change is that we have to declare a variable that
+    // indicates the @ref GlossMPICommunicator "MPI communicator" over
+    // which we are supposed to distribute our computations.
+    MPI_Comm mpi_communicator;
+
+    // Then we have two variables that tell us where in the parallel
+    // world we are. The first of the following variables,
+    // <code>n_mpi_processes</code> tells us how many MPI processes
+    // there exist in total, while the second one,
+    // <code>this_mpi_process</code>, indicates which is the number of
+    // the present process within this space of processes (in MPI
+    // language, this corresponds to the @ref GlossMPIRank "rank" of
+    // the process). The latter will have a unique value for each
+    // process between zero and (less than)
+    // <code>n_mpi_processes</code>. If this program is run on a
+    // single machine without MPI support, then their values are
+    // <code>1</code> and <code>0</code>, respectively.
+    const unsigned int n_mpi_processes;
+    const unsigned int this_mpi_process;
+
+    // Next up is a stream-like variable <code>pcout</code>. It is, in essence,
     // just something we use for convenience: in a parallel program,
     // if each process outputs status information, then there quickly
     // is a lot of clutter. Rather, we would want to only have one
@@ -140,7 +159,11 @@ namespace Step17
     // <code>operator&lt;&lt;</code>.
     ConditionalOStream pcout;
 
-    // The next few variables are taken verbatim from step-8:
+    // The remainder of the list of member variables is fundamentally the
+    // same as in step-8. However, we change the declarations of matrix
+    // and vector types to use parallel PETSc objects instead. Note that
+    // we do not use a separate sparsity pattern, since PETSc manages this
+    // internally as part of its matrix data structures.
     Triangulation<dim>   triangulation;
     DoFHandler<dim>      dof_handler;
 
@@ -148,36 +171,10 @@ namespace Step17
 
     ConstraintMatrix     hanging_node_constraints;
 
-    // In step-8, this would have been the place where we declared the
-    // member variables for the sparsity pattern, the system matrix,
-    // right hand, and solution vector. We change these declarations
-    // to use parallel PETSc objects instead. Note that we do not use
-    // a separate sparsity pattern, since PETSc manages that as part
-    // of its matrix data structures.
     PETScWrappers::MPI::SparseMatrix system_matrix;
 
     PETScWrappers::MPI::Vector       solution;
     PETScWrappers::MPI::Vector       system_rhs;
-
-    // The next change is that we have to declare a variable that
-    // indicates the @ref GlossMPICommunicator "MPI communicator" over
-    // which we are supposed to distribute our computations.
-    MPI_Comm mpi_communicator;
-
-    // Then we have two variables that tell us where in the parallel
-    // world we are. The first of the following variables,
-    // <code>n_mpi_processes</code> tells us how many MPI processes
-    // there exist in total, while the second one,
-    // <code>this_mpi_process</code>, indicates which is the number of
-    // the present process within this space of processes (in MPI
-    // language, this corresponds to the @ref GlossMPIRank "rank" of
-    // the process). The latter will have a unique value for each
-    // process between zero and (less than)
-    // <code>n_mpi_processes</code>. If this program is run on a
-    // single machine without MPI support, then their values are
-    // <code>1</code> and <code>0</code>, respectively.
-    const unsigned int n_mpi_processes;
-    const unsigned int this_mpi_process;
   };
 
 
@@ -260,23 +257,22 @@ namespace Step17
   // links a subset of all processes), and call the Utilities::MPI
   // helper functions to determine the number of processes and where
   // the present one fits into this picture. In addition, we make sure
-  // that output is only generated by the (globally) first process. As
-  // <code>this_mpi_process</code> is determined after creation of
-  // pcout, we cannot set the condition through the constructor,
-  // i.e. by <code>pcout(std::cout, this_mpi_process==0)</code>, but
-  // set the condition separately.
+  // that output is only generated by the (globally) first process.
+  // We do so by passing the stream we want to output to
+  // (<code>std::cout</code>) and a true/false flag as arguments where
+  // the latter is determined by testing whether the process currently
+  // executing the constructor call is the first in the MPI universe.
   template <int dim>
   ElasticProblem<dim>::ElasticProblem ()
     :
-    pcout (std::cout),
-    dof_handler (triangulation),
-    fe (FE_Q<dim>(1), dim),
     mpi_communicator (MPI_COMM_WORLD),
     n_mpi_processes (Utilities::MPI::n_mpi_processes(mpi_communicator)),
-    this_mpi_process (Utilities::MPI::this_mpi_process(mpi_communicator))
-  {
-    pcout.set_condition(this_mpi_process == 0);
-  }
+    this_mpi_process (Utilities::MPI::this_mpi_process(mpi_communicator)),
+    pcout (std::cout,
+           (this_mpi_process == 0)),
+    dof_handler (triangulation),
+    fe (FE_Q<dim>(1), dim)
+  {}