dtrtri(3S)

NAME
     DTRTRI - compute the inverse of a real upper or lower triangular matrix A

SYNOPSIS
     SUBROUTINE DTRTRI( UPLO, DIAG, N, A, LDA, INFO )

         CHARACTER      DIAG, UPLO

         INTEGER        INFO, LDA, N

         DOUBLE         PRECISION A( LDA, * )

IMPLEMENTATION
     These routines are part of the SCSL Scientific Library and can be loaded
     using either the -lscs or the -lscs_mp option.  The -lscs_mp option
     directs the linker to use the multi-processor version of the library.

     When linking to SCSL with -lscs or -lscs_mp, the default integer size is
     4 bytes (32 bits). Another version of SCSL is available in which integers
     are 8 bytes (64 bits).  This version allows the user access to larger
     memory sizes and helps when porting legacy Cray codes.  It can be loaded
     by using the -lscs_i8 option or the -lscs_i8_mp option. A program may use
     only one of the two versions; 4-byte integer and 8-byte integer library
     calls cannot be mixed.

PURPOSE
     DTRTRI computes the inverse of a real upper or lower triangular matrix A.
     This is the Level 3 BLAS version of the algorithm.


ARGUMENTS
     UPLO    (input) CHARACTER*1
             = 'U':  A is upper triangular;
             = 'L':  A is lower triangular.

     DIAG    (input) CHARACTER*1
             = 'N':  A is non-unit triangular;
             = 'U':  A is unit triangular.

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

     A       (input/output) DOUBLE PRECISION array, dimension (LDA,N)
             On entry, the triangular matrix A.  If UPLO = 'U', the leading
             N-by-N upper triangular part of the array A contains the upper
             triangular matrix, and the strictly lower triangular part of A is
             not referenced.  If UPLO = 'L', the leading N-by-N lower
             triangular part of the array A contains the lower triangular
             matrix, and the strictly upper triangular part of A is not
             referenced.  If DIAG = 'U', the diagonal elements of A are also
             not referenced and are assumed to be 1.  On exit, the
             (triangular) inverse of the original matrix, in the same storage
             format.

     LDA     (input) INTEGER
             The leading dimension of the array A.  LDA >= 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, A(i,i) is exactly zero.  The triangular matrix
             is singular and its inverse can not be computed.

SEE ALSO
     INTRO_LAPACK(3S), INTRO_SCSL(3S)

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