NAME

sgesv - compute the solution to a real system of linear equations  A ∗ X = B,

SYNOPSIS

SUBROUTINE SGESV(
N, NRHS, A, LDA, IPIV, B, LDB, INFO )

INTEGER INFO, LDA, LDB, N, NRHS

INTEGER IPIV( ∗ )

REAL A( LDA, ∗ ), B( LDB, ∗ )

PURPOSE

SGESV computes the solution to a real system of linear equations
   A ∗ X = B, where A is an N-by-N matrix and X and B are N-by-NRHS matrices.
 
The LU decomposition with partial pivoting and row interchanges is used to factor A as
   A = P ∗ L ∗ U,
where P is a permutation matrix, L is unit lower triangular, and U is upper triangular.  The factored form of A is then used to solve the system of equations A ∗ X = B.
 

ARGUMENTS

N       (input) INTEGER
The number of linear equations, i.e., the order of the matrix A.  N >= 0.

NRHS    (input) INTEGER
The number of right hand sides, i.e., the number of columns of the matrix B.  NRHS >= 0.

A       (input/output) REAL array, dimension (LDA,N)
On entry, the N-by-N coefficient matrix A. On exit, the factors L and U from the factorization A = P∗L∗U; the unit diagonal elements of L are not stored.

LDA     (input) INTEGER
The leading dimension of the array A.  LDA >= max(1,N).

IPIV    (output) INTEGER array, dimension (N)
The pivot indices that define the permutation matrix P; row i of the matrix was interchanged with row IPIV(i).

B       (input/output) REAL array, dimension (LDB,NRHS)
On entry, the N-by-NRHS matrix of right hand side matrix B. On exit, if INFO = 0, the N-by-NRHS solution matrix X.

LDB     (input) INTEGER
The leading dimension of the array B.  LDB >= max(1,N).

INFO    (output) INTEGER
= 0:  successful exit
< 0:  if INFO = -i, the i-th argument had an illegal value
> 0:  if INFO = i, U(i,i) is exactly zero.  The factorization has been completed, but the factor U is exactly singular, so the solution could not be computed.

SunSoft, Inc.  —  Last change: 27 Jun 1995