DTRTRI computes the inverse of a real upper or lower triangular


 matrix A.


 This is the Level 3 BLAS version of the algorithm.

UPLO

          UPLO is CHARACTER*1


          = 'U':  A is upper triangular;


          = 'L':  A is lower triangular.

DIAG

          DIAG is CHARACTER*1


          = 'N':  A is non-unit triangular;


          = 'U':  A is unit triangular.

N

          N is INTEGER


          The order of the matrix A.  N >= 0.

A

          A is 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

          LDA is INTEGER


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

INFO

          INFO is 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.

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

December 2016