NEIGHBORS_TO_METIS_GRAPH
Reformat Tet Mesh Neighbor File

NEIGHBORS_TO_METIS_GRAPH is a FORTRAN90 program which reads a file describing the graph-theoretic adjacency structure of the elements in a mesh of triangles or tetrahedrons and writes out a similar file that is suitable for input to the mesh partitioning program METIS.

Since we know we are dealing with a triangle or tet mesh, each "node" of the adjacency graph has 3 or 4 potential edges. If a potential edge is not used (in other words, if a face is a boundary face), then by convention we write out a "-1" for the neighbor value. Otherwise, the adjacency information lists the index of the element that is a neighbor on that face of the element

Converting to a METIS GRAPH format is trivial. We include an initial line that lists the number of "nodes" (elements) and "edges" (interfaces between pairs of elements), followed by, for each node (element), a list of the adjacent nodes (a list of the adjacent elements, omitting the "-1" values). A cross-eyed schoolboy sitting on a tack would be able to carry out this task!

Usage:

neighbors_to_metis_graph neighbor_file

reads the data in neighbor_file, rearranges it to suit METIS, and writes out the modified data to metis_graph_file

Licensing:

The computer code and data files described and made available on this web page are distributed under the GNU LGPL license.

Languages:

NEIGHBORS_TO_METIS_GRAPH is available in a C++ version and a FORTRAN90 version and a MATLAB version.

Related Programs:

GRAPHCHK, a C program which uses the METIS library to check that a METIS graph file has the proper format;

KMETIS, a C program which uses the METIS library to partition the nodes of a graph in a balanced way, useful for parallel processing;

METIS, a C library which partitions the nodes of a graph or the elements of a mesh, for division among a number of parallel processes, or to reorder the variables in a sparse matrix to minimize fillin;

METIS_GRAPH, a data directory which contains examples of METIS GRAPH files, the format for graphs to be read by METIS, which can partition a graph;

OEMETIS, a C program which uses the METIS library to reorder the variables in a sparse matrix.

ONMETIS, a C program which uses the METIS library to reorder the variables in a sparse matrix.

TET_MESH_TET_NEIGHBORS, a FORTRAN90 program which reads information about a tet mesh and writes out a list of the tetrahedrons that are adjacent to a given tetrahedron;

TRIANGULATION_TRIANGLE_NEIGHBORS, a FORTRAN90 program which reads data defining a triangulation, determines the neighboring triangles of each triangle, and writes that information to a file.

Reference:

1. George Karypis, Vipin Kumar,
   METIS, a Software Package for Partitioning Unstructured Graphs and Computing Fill-Reduced Orderings of Sparse Matrices;

Source Code:

• neighbors_to_metis_graph.f90, the source code.

Examples and Tests:

• cube_tetra.neighbors, a sample tet mesh neighbor file that can be used as input to the program.
• cube_tetra.metis_graph, the modified tet mesh neighbor file created by the program, suitable for input to METIS.

List of Routines:

• MAIN is the main program for NEIGHBORS_TO_METIS_GRAPH.
• CH_CAP capitalizes a single character.
• CH_EQI is a case insensitive comparison of two characters for equality.
• CH_TO_DIGIT returns the integer value of a base 10 digit.
• FILE_COLUMN_COUNT counts the number of columns in the first line of a file.
• FILE_NAME_EXT_GET determines the "extension" of a file name.
• FILE_NAME_EXT_SWAP replaces the current "extension" of a file name.
• FILE_ROW_COUNT counts the number of row records in a file.
• GET_UNIT returns a free FORTRAN unit number.
• I4COL_COMPARE compares columns I and J of a integer array.
• I4COL_SORT_A ascending sorts an integer array of columns.
• I4COL_SWAP swaps columns J1 and J2 of a integer array of column data.
• I4I4I4_SORT_A ascending sorts a triple of integers.
• I4MAT_TRANSPOSE_PRINT prints an I4MAT, transposed.
• I4MAT_TRANSPOSE_PRINT_SOME prints some of the transpose of an I4MAT.
• ITABLE_DATA_READ reads data from an integer table file.
• ITABLE_HEADER_READ reads the header from an integer table file.
• METIS_GRAPH_WRITE writes the METIS graph file.
• S_BLANK_DELETE removes blanks from a string, left justifying the remainder.
• S_INDEX_LAST_C finds the LAST occurrence of a given character.
• S_TO_I4 reads an integer value from a string.
• S_TO_I4VEC reads an I4VEC from a string.
• S_WORD_COUNT counts the number of "words" in a string.
• SORT_HEAP_EXTERNAL externally sorts a list of items into ascending order.
• TIMESTAMP prints the current YMDHMS date as a time stamp.

You can go up one level to the FORTRAN90 source codes.