STRTI2 (3lapack)

compute the inverse of a real upper or lower triangular matrix

SYNOPSIS

  SUBROUTINE STRTI2( UPLO, DIAG, N, A, LDA, INFO )

      CHARACTER      DIAG, UPLO

      INTEGER        INFO, LDA, N

      REAL           A( LDA, * )

PURPOSE

  STRTI2 computes the inverse of a real upper or lower triangular matrix.

  This is the Level 2 BLAS version of the algorithm.

ARGUMENTS

  UPLO    (input) CHARACTER*1
          Specifies whether the matrix A is upper or lower triangular.  =
          'U':  Upper triangular
          = 'L':  Lower triangular

  DIAG    (input) CHARACTER*1
          Specifies whether or not the matrix A is unit triangular.  = 'N':
          Non-unit triangular
          = 'U':  Unit triangular

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

  A       (input/output) REAL 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 = -k, the k-th argument had an illegal value