Improved the documentation of hypre_AMSSetInteriorNodes().

docs/usr_solvers.tex

@@ -708,7 +708,8 @@ nodes which are interior to a zero-conductivity region provided by the function
 \begin{display}\begin{verbatim}
 HYPRE_AMSSetInteriorNodes(solver, HYPRE_ParVector interior_nodes);
 \end{verbatim}\end{display}
-Based on the \code{interior_nodes} variable, a restricted discrete gradient
+A node is interior, if its entry in the \code{interior_nodes} array is $1.0$.
+Based on this array, a restricted discrete gradient
 operator $G_0$ is constructed, and AMS is then defined based on the matrix
 ${\mathbf A}+\delta G_0^TG_0$ which is non-singular, and a small $\delta>0$ perturbation of
 ${\mathbf A}$. When iterating with this preconditioner, it is advantageous to project on

parcsr_ls/HYPRE_parcsr_ls.h

@@ -1597,8 +1597,8 @@ HYPRE_Int HYPRE_AMSSetBetaPoissonMatrix(HYPRE_Solver       solver,
 /**
  * (Optional) Set the list of nodes which are interior to a zero-conductivity
  * region. This way, a more robust solver is constructed, that can be iterated
- * to lower tolerance levels. This function should be called before
- * HYPRE\_AMSSetup()!
+ * to lower tolerance levels. A node is interior if its entry in the array is
+ * 1.0. This function should be called before HYPRE\_AMSSetup()!
  **/
 HYPRE_Int HYPRE_AMSSetInteriorNodes(HYPRE_Solver    solver,
                                     HYPRE_ParVector interior_nodes);

parcsr_ls/ams.c

@@ -1118,6 +1118,7 @@ HYPRE_Int hypre_AMSSetBetaPoissonMatrix(void *solver,
  * hypre_AMSSetInteriorNodes
  *
  * Set the list of nodes which are interior to the zero-conductivity region.
+ * A node is interior if interior_nodes[i] == 1.0.
  *
  * Should be called before hypre_AMSSetup()!
  *--------------------------------------------------------------------------*/
@@ -1963,7 +1964,9 @@ HYPRE_Int hypre_AMSSetup(void *solver,
       ams_data -> solve_counter = 0;
 
       /* Construct the discrete gradient matrix for the zero-conductivity region
-         by eliminating the zero-conductivity nodes from G^t */
+         by eliminating the zero-conductivity nodes from G^t. The range of G0
+         represents the kernel of A, i.e. the gradients of nodal basis functions
+         supported in zero-conductivity regions. */
       hypre_ParCSRMatrixTranspose(ams_data -> G, &G0t, 1);
       {
          HYPRE_Int i, j;