private static void Main(string[] args)
//****************************************************************************80
//
// Purpose:
//
// MAIN is the main program for FEM2D_POISSON_CG.
//
// Discussion:
//
// This program is a variant of FEM2D_POISSON. That program is
// particularly limited because of its use of banded matrix storage and
// solving routines.
//
// This program discards the banded approach. Instead, it uses a
// sparse matrix storage format and a conjugate gradient solver,
// which allow this program to solve larger problems faster.
//
// This program solves the Poisson equation
//
// -DEL H(X,Y) DEL U(X,Y) + K(X,Y) * U(X,Y) = F(X,Y)
//
// in a triangulated region in the plane.
//
// Along the boundary of the region, Dirichlet conditions
// are imposed:
//
// U(X,Y) = G(X,Y)
//
// The code uses continuous piecewise linear basis functions on
// triangles.
//
// Problem specification:
//
// The user defines the geometry by supplying two data files
// which list the node coordinates, and list the nodes that make up
// each element.
//
// The user specifies the right hand side of the Dirichlet boundary
// conditions by supplying a function
//
// void dirichlet_condition ( int node_num, double node_xy[2*node_num],
// double node_bc[node_num] )
//
// The user specifies the coefficient function H(X,Y) of the Poisson
// equation by supplying a routine of the form
//
// void h_coef ( int node_num, double node_xy[2*node_num],
// double node_h[node_num] )
//
// The user specifies the coefficient function K(X,Y) of the Poisson
// equation by supplying a routine of the form
//
// void k_coef ( int node_num, double node_xy[2*node_num],
// double node_k[node_num] )
//
// The user specifies the right hand side of the Poisson equation
// by supplying a routine of the form
//
// void rhs ( int node_num, double node_xy[2*node_num],
// double node_f[node_num] )
//
// Usage:
//
// fem2d_poisson_cg prefix
//
// where 'prefix' is the common filename prefix so that:
//
// * prefix_nodes.txt contains the coordinates of the nodes;
// * prefix_elements.txt contains the indices of nodes forming each element.
//
// Files created include:
//
// * prefix_nodes.eps, an image of the nodes;
// * prefix_elements.eps, an image of the elements;
// * prefix_values.txt, the value of the solution at every node.
//
// Licensing:
//
// This code is distributed under the GNU LGPL license.
//
// Modified:
//
// 25 January 2013
//
// Author:
//
// John Burkardt
//
// Local parameters:
//
// Local, double A[NZ_NUM], the coefficient matrix.
//
// Local, int ELEMENT_NODE[3*ELEMENT_NUM];
// ELEMENT_NODE(I,J) is the global index of local node I in element J.
//
// Local, int ELEMENT_NUM, the number of elements.
//
// Local, integer ELEMENT_ORDER, the element order.
//
// Local, double F[NODE_NUM], the right hand side.
//
// Local, int IA[NZ_NUM], the row indices of the nonzero entries
// of the coefficient matrix.
//
// Local, int JA[NZ_NUM], the column indices of the nonzero entries
// of the coefficient matrix.
//
// Local, bool NODE_BOUNDARY[NODE_NUM], is TRUE if the node is
// found to lie on the boundary of the region.
//
// Local, int NODE_CONDITION[NODE_NUM],
// indicates the condition used to determine the variable at a node.
// 0, there is no condition (and no variable) at this node.
// 1, a finite element equation is used;
// 2, a Dirichlet condition is used.
// 3, a Neumann condition is used.
//
// Local, int NODE_NUM, the number of nodes.
//
// Local, double NODE_U[NODE_NUM], the finite element coefficients.
//
// Local, double NODE_XY[2*NODE_NUM], the coordinates of nodes.
//
// Local, int NZ_NUM, the number of nonzero entries
// in the coefficient matrix.
//
// Local, integer QUAD_NUM, the number of quadrature points used for
// assembly. This is currently set to 3, the lowest reasonable value.
// Legal values are 1, 3, 4, 6, 7, 9, 13, and for some problems, a value
// of QUAD_NUM greater than 3 may be appropriate.
//
{
const bool debug = false;
int node;
string prefix;
const int quad_num = 3;
Console.WriteLine("");
Console.WriteLine("FEM2D_POISSON_CG:");
Console.WriteLine("");
Console.WriteLine(" A version of FEM2D_POISSON using sparse storage");
Console.WriteLine(" and a conjugate gradient solver.");
Console.WriteLine("");
Console.WriteLine(" Solution of the Poisson equation in an arbitrary region");
Console.WriteLine(" in 2 dimensions.");
Console.WriteLine("");
Console.WriteLine(" - DEL H(x,y) DEL U(x,y) + K(x,y) * U(x,y) = F(x,y) in the region");
Console.WriteLine("");
Console.WriteLine(" U(x,y) = G(x,y) on the boundary.");
Console.WriteLine("");
Console.WriteLine(" The finite element method is used,");
Console.WriteLine(" with triangular elements,");
Console.WriteLine(" which must be a 3 node linear triangle.");
//
// Get the filename prefix.
//
try
{
prefix = args[0];
}
catch
{
Console.WriteLine("");
Console.WriteLine(" Please enter the filename prefix:");
prefix = Console.ReadLine();
}
if (prefix != "baffle" && prefix != "ell" && prefix != "lake")
{
Console.WriteLine("Supported prefix value in this test is one of : baffle, ell, lake");
return;
}
//
// Create the file names.
//
string node_filename = prefix + "_nodes.txt";
string element_filename = prefix + "_elements.txt";
string solution_filename = prefix + "_values.txt";
Console.WriteLine("");
Console.WriteLine(" Node file is \"" + node_filename + "\".");
Console.WriteLine(" Element file is \"" + element_filename + "\".");
//
// Read the node coordinate file.
//
TableHeader h = typeMethods.r8mat_header_read(node_filename);
int dim_num = h.m;
int node_num = h.n;
Console.WriteLine(" Number of nodes = " + node_num + "");
int[] node_condition = new int[node_num];
double[] node_xy = typeMethods.r8mat_data_read(node_filename, dim_num, node_num);
typeMethods.r8mat_transpose_print_some(dim_num, node_num, node_xy, 1, 1, 2, 10,
" First 10 nodes");
//
// Read the triangle description file.
//
h = typeMethods.i4mat_header_read(element_filename);
int element_order = h.m;
int element_num = h.n;
Console.WriteLine("");
Console.WriteLine(" Element order = " + element_order + "");
Console.WriteLine(" Number of elements = " + element_num + "");
if (element_order != 3)
{
Console.WriteLine("");
Console.WriteLine("FEM2D_POISSON_CG - Fatal error!");
Console.WriteLine(" The input triangulation has order " + element_order + "");
Console.WriteLine(" However, a triangulation of order 3 is required.");
return;
}
int[] element_node = typeMethods.i4mat_data_read(element_filename, element_order,
element_num);
typeMethods.i4mat_transpose_print_some(3, element_num,
element_node, 1, 1, 3, 10, " First 10 elements");
Console.WriteLine("");
Console.WriteLine(" Quadrature order = " + quad_num + "");
//
// Determine which nodes are boundary nodes and which have a
// finite element unknown. Then set the boundary values.
//
bool[] node_boundary = Boundary.triangulation_order3_boundary_node(node_num, element_num,
element_node);
//
// Determine the node conditions.
// For now, we'll just assume all boundary nodes are Dirichlet.
//
for (node = 0; node < node_num; node++)
{
node_condition[node] = node_boundary[node] switch
{
true => 2,
_ => 1
};
}
//
// Determine the element neighbor array, just so we can estimate
// the nonzeros.
//
int[] element_neighbor = Neighbor.triangulation_order3_neighbor_triangles(element_num, element_node);
//
// Count the number of nonzeros.
//
int[] adj_col = new int[node_num + 1];
int nz_num = Adjacency.triangulation_order3_adj_count(node_num, element_num,
element_node, element_neighbor, adj_col);
Console.WriteLine("");
Console.WriteLine(" Number of nonzero coefficients NZ_NUM = " + nz_num + "");
//
// Set up the sparse row and column index vectors.
//
int[] ia = new int[nz_num];
int[] ja = new int [nz_num];
Adjacency.triangulation_order3_adj_set2(node_num, element_num, element_node,
element_neighbor, nz_num, adj_col, ia, ja);
switch (debug)
{
case true:
typeMethods.i4vec2_print(nz_num, ia, ja, " Adjacency pairs:");
break;
}
//
// Index the diagonal elements for use by the CG solver.
//
int[] diag = Diagonal.diag_index(nz_num, ia, ja, node_num);
switch (debug)
{
case true:
typeMethods.i4vec_print(node_num, diag, " Diagonal adjacency vector:");
break;
}
//
// Allocate space for the coefficient matrix A and right hand side F.
//
double[] a = new double[nz_num];
double[] f = new double[node_num];
double[] node_u = new double[node_num];
//
// Assemble the finite element coefficient matrix A and the right-hand side F.
//
switch (prefix)
{
case "baffle":
DSP.assemble_poisson_dsp(node_num, node_xy, element_num,
element_node, quad_num, nz_num, ia, ja, ref a, ref f, baffle.rhs, baffle.h_coef, baffle.k_coef);
break;
case "ell":
DSP.assemble_poisson_dsp(node_num, node_xy, element_num,
element_node, quad_num, nz_num, ia, ja, ref a, ref f, ell.rhs, ell.h_coef, ell.k_coef);
break;
case "lake":
DSP.assemble_poisson_dsp(node_num, node_xy, element_num,
element_node, quad_num, nz_num, ia, ja, ref a, ref f, lake.rhs, lake.h_coef, lake.k_coef);
break;
}
switch (debug)
{
//
// Print a portion of the matrix.
//
case true:
DSP.dsp_print_some(node_num, node_num, nz_num, ia, ja, a, 1, 1, 10, 10,
" Part of Finite Element matrix A:");
typeMethods.r8vec_print_some(node_num, f, 1, 10,
" Part of right hand side vector F:");
break;
}
//
// Adjust the linear system to account for Dirichlet boundary conditions.
//
switch (prefix)
{
case "baffle":
DSP.dirichlet_apply_dsp(node_num, node_xy, node_condition, nz_num, ia, ja,
ref a, ref f, baffle.dirichlet_condition);
break;
case "ell":
DSP.dirichlet_apply_dsp(node_num, node_xy, node_condition, nz_num, ia, ja,
ref a, ref f, ell.dirichlet_condition);
break;
case "lake":
DSP.dirichlet_apply_dsp(node_num, node_xy, node_condition, nz_num, ia, ja,
ref a, ref f, lake.dirichlet_condition);
break;
}
switch (debug)
{
case true:
DSP.dsp_print_some(node_num, node_num, nz_num, ia, ja, a, 1, 1, 10, 10,
" Part of finite Element matrix A after boundary adjustments:");
typeMethods.r8vec_print_some(node_num, f, 1, 10,
" Part of right hand side vector F:");
break;
}
//
// Solve the linear system using the conjugate gradient method.
//
node_u = ConjugateGradient.solve_cg(node_num, diag, nz_num, ia, ja, a, f);
typeMethods.r8vec_print_some(node_num, node_u, 1, 10,
" Part of the solution vector vector U:");
//
// Write an ASCII file that can be read into MATLAB.
//
typeMethods.r8mat_write(solution_filename, 1, node_num, node_u);
Console.WriteLine("");
Console.WriteLine(" Wrote an ASCII file");
Console.WriteLine(" \"" + solution_filename + "\".");
Console.WriteLine(" of the form");
Console.WriteLine(" U ( X(I), Y(I) )");
Console.WriteLine(" which can be used for plotting.");
switch (debug)
{
case true:
typeMethods.r8vec_print_some(node_num, node_u, 1, 10,
" Part of the solution vector:");
break;
}
Console.WriteLine("");
Console.WriteLine("FEM2D_POISSON_CG:");
Console.WriteLine(" Normal end of execution.");
Console.WriteLine("");
}
}