Contents

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

NAME

     dgecon - estimate the reciprocal of the condition number  of
     a  general  real  matrix  A,  in  either  the  1-norm or the
     infinity-norm, using the LU factorization computed by SGETRF

SYNOPSIS

     SUBROUTINE DGECON(NORM, N, A, LDA, ANORM, RCOND, WORK, WORK2, INFO)

     CHARACTER * 1 NORM
     INTEGER N, LDA, INFO
     INTEGER WORK2(*)
     DOUBLE PRECISION ANORM, RCOND
     DOUBLE PRECISION A(LDA,*), WORK(*)

     SUBROUTINE DGECON_64(NORM, N, A, LDA, ANORM, RCOND, WORK, WORK2,
           INFO)

     CHARACTER * 1 NORM
     INTEGER*8 N, LDA, INFO
     INTEGER*8 WORK2(*)
     DOUBLE PRECISION ANORM, RCOND
     DOUBLE PRECISION A(LDA,*), WORK(*)

  F95 INTERFACE
     SUBROUTINE GECON(NORM, [N], A, [LDA], ANORM, RCOND, [WORK], [WORK2],
            [INFO])

     CHARACTER(LEN=1) :: NORM
     INTEGER :: N, LDA, INFO
     INTEGER, DIMENSION(:) :: WORK2
     REAL(8) :: ANORM, RCOND
     REAL(8), DIMENSION(:) :: WORK
     REAL(8), DIMENSION(:,:) :: A

     SUBROUTINE GECON_64(NORM, [N], A, [LDA], ANORM, RCOND, [WORK], [WORK2],
            [INFO])

     CHARACTER(LEN=1) :: NORM
     INTEGER(8) :: N, LDA, INFO
     INTEGER(8), DIMENSION(:) :: WORK2
     REAL(8) :: ANORM, RCOND
     REAL(8), DIMENSION(:) :: WORK
     REAL(8), DIMENSION(:,:) :: A

  C INTERFACE
     #include <sunperf.h>
     void dgecon(char norm, int n, double  *a,  int  lda,  double
               anorm, double *rcond, int *info);

     void dgecon_64(char norm, long n, double *a, long lda,  dou-
               ble anorm, double *rcond, long *info);

PURPOSE

     dgecon estimates the reciprocal of the condition number of a
     general   real  matrix  A,  in  either  the  1-norm  or  the
     infinity-norm,  using  the  LU  factorization  computed   by
     SGETRF.

     An estimate is obtained for norm(inv(A)), and the reciprocal
     of the condition number is computed as
        RCOND = 1 / ( norm(A) * norm(inv(A)) ).

ARGUMENTS

     NORM (input)
               Specifies whether the 1-norm condition  number  or
               the infinity-norm condition number is required:
               = '1' or 'O':  1-norm;
               = 'I':         Infinity-norm.

     N (input) The order of the matrix A.  N >= 0.

     A (input) The factors L and U from  the  factorization  A  =
               P*L*U as computed by SGETRF.

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

     ANORM (input)
               If NORM = '1' or 'O', the 1-norm of  the  original
               matrix A.  If NORM = 'I', the infinity-norm of the
               original matrix A.

     RCOND (output)
               The reciprocal of  the  condition  number  of  the
               matrix   A,  computed  as  RCOND  =  1/(norm(A)  *
               norm(inv(A))).

     WORK (workspace)
               dimension(4*N)

     WORK2 (workspace)
               dimension(N)

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