PETSc
FORTRAN77 Examples

This directory includes examples of the use of PETSc with a calling program written in FORTRAN77.

PETSc is a library of high level mathematical routines that can be executed in a parallel environment, making it easier for a user to gain the advantages of MPI.

PETSc stands for the Portable Extensible Toolkit for Scientific Computations.

PETSc is particularly suitable for the numerical solution of systems of partial differential equations on high performance computers. PETSc includes parallel linear and nonlinear equation solvers and time integrators that may be used by application programs written in C, C++, FORTRAN77 or FORTRAN90.

PETSc consists of a number of libraries which work with a particular family of objects, such as vectors. Some of the PETSc modules deal with

• index sets, including permutations;
• vectors;
• matrices, especially sparse matrices;
• distributed arrays, as when the data for a single matrix is distributed over a set of processors;
• Krylov subspace methods for solving linear systems;
• preconditioners for linear algebra systems, including multigrid and sparse direct solvers;
• solvers for systems of nonlinear equations;
• partial differential equation solvers;
• time steppers for time-dependent partial differential equations;

PETSc includes parts of the following software libraries:

• BLAS1 vector library,
• BLAS2 matrix-vector library,
• BLAS3 matrix-matrix library,
• LAPACK linear algebra library,
• LIBTFS, an efficient parallel direct solver of Henry Tufo and Paul Fischer,
• LINPACK linear algebra library,
• MINPACK minimization library,
• SPARSEKIT2, Yousef Saad's sparse matrix library,
• SPARSEPAK, matrix reordering routines.

PETSc runs in parallel by relying on:

• MPI, the message-passing interface library,

A FORTRAN77 program that uses PETSc must specify many include files, from the basis level up to the level corresponding to the highest level PETSc objects needed within that program. That means that the user source code will include statements like

#include "include/finclude/petsc.h" #include "include/finclude/petscvec.h" #include "include/finclude/petscmat.h" #include "include/finclude/petscksp.h" #include "include/finclude/petscpc.h"

Usage:

Before using PETSc, the user must set the environment variable PETSC_DIR, indicating the full path of the PETSc home directory. On Phoenix, for instance, this might be done with the command

setenv PETSC_DIR /usr/local/petsc

Before using PETSc, the user must set the environment variable PETSC_ARCH, indicating the architecture of the machine on which PETSc is to be run. On Phoenix, for instance, this might be done with the command

setenv PETSC_ARCH linux-gnu

The commands required to compile, link and load a program with PETSc are complicated. It is best to use a makefile for this purpose, in which case most of the complications can be hidden. A bare bones makefile for the example ex1.F, which is going to use PETSc's Krylov Subspace Package (KSP), would look like this:

include ${PETSC_DIR}/bmake/common/base

ex1: ex1.o
	-${FLINKER} -o ex1 ex1.o ${PETSC_FORTRAN_LIB} ${PETSC_LIB}
      

make ex1

The mpirun command may be used for SMALL jobs that run for a SHORT time on FEW processors. Repeated use of the mpirun command for large long jobs is an abuse of the system and will not be allowed.

To run a program that uses PETSc, the user may invoke the mpirun command, specifying the number of processors.

mpirun -np 4 ex1

To run a program that uses PETSc, the CONDOR system is preferable. This is a batch system which tries to be fair and efficient in the allocation of computing resources. To use CONDOR, the user should create an executable program, then prepare a "CONDOR submit script" that describes how the executable is to be run, and on how many processors, and submit the script. Details and examples of how to do this are given on the CONDOR examples page.

Related Data and Programs:

BLAS1, a vector-vector library, is included in PETSC.

BLAS2, a matrix-vector library, is included in PETSC.

BLAS3, a matrix-matrix library, is included in PETSC.

CONDOR, is a queueing system used locally to submit jobs to our parallel clusters.

LAPACK, an extensive linear algebra library, is included in PETSC.

LINPACK, an extensive linear algebra library, is included in PETSC.

MINPACK, a library for minimization and least squares, is included in PETSC.

MPI is used as part of the PETSC library. You may be interested in seeing examples of that parallel programming system.

PESSL is a parallel mathematics library developed exclusively for IBM systems.

PETSc examples are also available in a C version, and a C++ version, and a FORTRAN90 version.

SPARSEKIT2, Yousef Saad's library for sparse matrices, is included in PETSC.