dgesv (l)  Linux Manuals
dgesv: computes the solution to a real system of linear equations A * X = B,
NAME
DGESV  computes the solution to a real system of linear equations A * X = B,SYNOPSIS
 SUBROUTINE DGESV(
 N, NRHS, A, LDA, IPIV, B, LDB, INFO )
 INTEGER INFO, LDA, LDB, N, NRHS
 INTEGER IPIV( * )
 DOUBLE PRECISION A( LDA, * ), B( LDB, * )
PURPOSE
DGESV computes the solution to a real system of linear equationsA
A
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) DOUBLE PRECISION array, dimension (LDA,N)
 On entry, the NbyN 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) DOUBLE PRECISION array, dimension (LDB,NRHS)
 On entry, the NbyNRHS matrix of right hand side matrix B. On exit, if INFO = 0, the NbyNRHS 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 ith 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.