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dtrtrs

 NAME
      DTRTRS - solve a triangular system of the form   A * X = B
      or A**T * X = B,

 SYNOPSIS
      SUBROUTINE DTRTRS( UPLO, TRANS, DIAG, N, NRHS, A, LDA, B,
                         LDB, INFO )

          CHARACTER      DIAG, TRANS, UPLO

          INTEGER        INFO, LDA, LDB, N, NRHS

          DOUBLE         PRECISION A( LDA, * ), B( LDB, * )

 PURPOSE
      DTRTRS solves a triangular system of the form

      where A is a triangular matrix of order N, and B is an N-
      by-NRHS matrix.  A check is made to verify that A is non-
      singular.

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

      TRANS   (input) CHARACTER*1
              Specifies the form of the system of equations:
              = 'N':  A * X = B  (No transpose)
              = 'T':  A**T * X = B  (Transpose)
              = 'C':  A**H * X = B  (Conjugate transpose = Tran-
              spose)

      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.

      NRHS    (input) INTEGER
              The number of right hand sides, i.e., the number of
              columns of the matrix B.  NRHS >= 0.

      A       (input) DOUBLE PRECISION array, dimension (LDA,N)
              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.

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

 (LDB,NRHS)
      B       (input/output) DOUBLE PRECISION array, dimension
              On entry, the right hand side matrix B.  On exit, if
              INFO = 0, the solution matrix X.

      LDB     (input) INTEGER
              The leading dimension of the array B.  LDB >=
              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, the i-th diagonal element of A is
              zero, indicating that the matrix is singular and the
              solutions X have not been computed.