Contents

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

NAME

     dsytri - compute the inverse of a real symmetric  indefinite
     matrix  A  using  the  factorization  A  =  U*D*U**T  or A =
     L*D*L**T computed by DSYTRF

SYNOPSIS

     SUBROUTINE DSYTRI(UPLO, N, A, LDA, IPIVOT, WORK, INFO)

     CHARACTER * 1 UPLO
     INTEGER N, LDA, INFO
     INTEGER IPIVOT(*)
     DOUBLE PRECISION A(LDA,*), WORK(*)

     SUBROUTINE DSYTRI_64(UPLO, N, A, LDA, IPIVOT, WORK, INFO)

     CHARACTER * 1 UPLO
     INTEGER*8 N, LDA, INFO
     INTEGER*8 IPIVOT(*)
     DOUBLE PRECISION A(LDA,*), WORK(*)

  F95 INTERFACE
     SUBROUTINE SYTRI(UPLO, N, A, [LDA], IPIVOT, [WORK], [INFO])

     CHARACTER(LEN=1) :: UPLO
     INTEGER :: N, LDA, INFO
     INTEGER, DIMENSION(:) :: IPIVOT
     REAL(8), DIMENSION(:) :: WORK
     REAL(8), DIMENSION(:,:) :: A

     SUBROUTINE SYTRI_64(UPLO, N, A, [LDA], IPIVOT, [WORK], [INFO])

     CHARACTER(LEN=1) :: UPLO
     INTEGER(8) :: N, LDA, INFO
     INTEGER(8), DIMENSION(:) :: IPIVOT
     REAL(8), DIMENSION(:) :: WORK
     REAL(8), DIMENSION(:,:) :: A

  C INTERFACE
     #include <sunperf.h>

     void dsytri(char uplo,  int  n,  double  *a,  int  lda,  int
               *ipivot, int *info);

     void dsytri_64(char uplo, long n, double *a, long lda,  long
               *ipivot, long *info);

PURPOSE

     dsytri computes the inverse of a real  symmetric  indefinite
     matrix  A  using  the  factorization  A  =  U*D*U**T  or A =
     L*D*L**T computed by DSYTRF.

ARGUMENTS

     UPLO (input)
               Specifies whether the details of the factorization
               are stored as an upper or lower triangular matrix.
               = 'U':  Upper triangular, form is A = U*D*U**T;
               = 'L':  Lower triangular, form is A = L*D*L**T.

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

     A (input/output)
               On entry, the block diagonal matrix D and the mul-
               tipliers  used to obtain the factor U or L as com-
               puted by DSYTRF.

               On exit, if INFO = 0, the (symmetric)  inverse  of
               the  original  matrix.   If  UPLO = 'U', the upper
               triangular part of the inverse is formed  and  the
               part of A below the diagonal is not referenced; if
               UPLO =  'L'  the  lower  triangular  part  of  the
               inverse  is  formed  and  the  part of A above the
               diagonal is not referenced.

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

     IPIVOT (input)
               Details of the interchanges and the  block  struc-
               ture of D as determined by DSYTRF.

     WORK (workspace)
               dimension(N)

     INFO (output)
               = 0: successful exit
               < 0: if INFO = -i, the i-th argument had an  ille-
               gal value
               > 0: if INFO = i, D(i,i) = 0; the matrix is singu-
               lar and its inverse could not be computed.