Contents

• NAME
• SYNOPSIS
  • F95 INTERFACE
  • C INTERFACE
• PURPOSE
• ARGUMENTS

NAME

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

SYNOPSIS

     SUBROUTINE DGESV(N, NRHS, A, LDA, IPIVOT, B, LDB, INFO)

     INTEGER N, NRHS, LDA, LDB, INFO
     INTEGER IPIVOT(*)
     DOUBLE PRECISION A(LDA,*), B(LDB,*)

     SUBROUTINE DGESV_64(N, NRHS, A, LDA, IPIVOT, B, LDB, INFO)

     INTEGER*8 N, NRHS, LDA, LDB, INFO
     INTEGER*8 IPIVOT(*)
     DOUBLE PRECISION A(LDA,*), B(LDB,*)

  F95 INTERFACE
     SUBROUTINE GESV([N], [NRHS], A, [LDA], IPIVOT, B, [LDB], [INFO])

     INTEGER :: N, NRHS, LDA, LDB, INFO
     INTEGER, DIMENSION(:) :: IPIVOT
     REAL(8), DIMENSION(:,:) :: A, B

     SUBROUTINE GESV_64([N], [NRHS], A, [LDA], IPIVOT, B, [LDB], [INFO])

     INTEGER(8) :: N, NRHS, LDA, LDB, INFO
     INTEGER(8), DIMENSION(:) :: IPIVOT
     REAL(8), DIMENSION(:,:) :: A, B

  C INTERFACE
     #include <sunperf.h>

     void dgesv(int n, int nrhs, double *a, int lda, int *ipivot,
               double *b, int ldb, int *info);

     void dgesv_64(long n, long nrhs, double *a, long  lda,  long
               *ipivot, double *b, long ldb, long *info);

PURPOSE

     dgesv computes the solution to a real system of linear equa-
     tions
        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) The number of linear equations, i.e., the order of
               the matrix A.  N >= 0.

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

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

     IPIVOT (output)
               The pivot  indices  that  define  the  permutation
               matrix  P;  row  i  of the matrix was interchanged
               with row IPIVOT(i).

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

     INFO (output)
               = 0:  successful exit
               < 0:  if INFO = -i, the i-th argument had an ille-
               gal 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.