NAME

       dlaqtr.f -

SYNOPSIS

   Functions/Subroutines
       subroutine dlaqtr (LTRAN, LREAL, N, T, LDT, B, W, SCALE, X, WORK, INFO)
           DLAQTR solves a real quasi-triangular system of equations, or a complex quasi-
           triangular system of special form, in real arithmetic.

Function/Subroutine Documentation

   subroutine dlaqtr (logicalLTRAN, logicalLREAL, integerN, double precision, dimension( ldt, *
       )T, integerLDT, double precision, dimension( * )B, double precisionW, double
       precisionSCALE, double precision, dimension( * )X, double precision, dimension( * )WORK,
       integerINFO)
       DLAQTR solves a real quasi-triangular system of equations, or a complex quasi-triangular
       system of special form, in real arithmetic.

       Purpose:

            DLAQTR solves the real quasi-triangular system

                         op(T)*p = scale*c,               if LREAL = .TRUE.

            or the complex quasi-triangular systems

                       op(T + iB)*(p+iq) = scale*(c+id),  if LREAL = .FALSE.

            in real arithmetic, where T is upper quasi-triangular.
            If LREAL = .FALSE., then the first diagonal block of T must be
            1 by 1, B is the specially structured matrix

                           B = [ b(1) b(2) ... b(n) ]
                               [       w            ]
                               [           w        ]
                               [              .     ]
                               [                 w  ]

            op(A) = A or A**T, A**T denotes the transpose of
            matrix A.

            On input, X = [ c ].  On output, X = [ p ].
                          [ d ]                  [ q ]

            This subroutine is designed for the condition number estimation
            in routine DTRSNA.

       Parameters:
           LTRAN

                     LTRAN is LOGICAL
                     On entry, LTRAN specifies the option of conjugate transpose:
                        = .FALSE.,    op(T+i*B) = T+i*B,
                        = .TRUE.,     op(T+i*B) = (T+i*B)**T.

           LREAL

                     LREAL is LOGICAL
                     On entry, LREAL specifies the input matrix structure:
                        = .FALSE.,    the input is complex
                        = .TRUE.,     the input is real

           N

                     N is INTEGER
                     On entry, N specifies the order of T+i*B. N >= 0.

           T

                     T is DOUBLE PRECISION array, dimension (LDT,N)
                     On entry, T contains a matrix in Schur canonical form.
                     If LREAL = .FALSE., then the first diagonal block of T mu
                     be 1 by 1.

           LDT

                     LDT is INTEGER
                     The leading dimension of the matrix T. LDT >= max(1,N).

           B

                     B is DOUBLE PRECISION array, dimension (N)
                     On entry, B contains the elements to form the matrix
                     B as described above.
                     If LREAL = .TRUE., B is not referenced.

           W

                     W is DOUBLE PRECISION
                     On entry, W is the diagonal element of the matrix B.
                     If LREAL = .TRUE., W is not referenced.

           SCALE

                     SCALE is DOUBLE PRECISION
                     On exit, SCALE is the scale factor.

           X

                     X is DOUBLE PRECISION array, dimension (2*N)
                     On entry, X contains the right hand side of the system.
                     On exit, X is overwritten by the solution.

           WORK

                     WORK is DOUBLE PRECISION array, dimension (N)

           INFO

                     INFO is INTEGER
                     On exit, INFO is set to
                        0: successful exit.
                          1: the some diagonal 1 by 1 block has been perturbed by
                             a small number SMIN to keep nonsingularity.
                          2: the some diagonal 2 by 2 block has been perturbed by
                             a small number in DLALN2 to keep nonsingularity.
                     NOTE: In the interests of speed, this routine does not
                           check the inputs for errors.

       Author:
           Univ. of Tennessee

           Univ. of California Berkeley

           Univ. of Colorado Denver

           NAG Ltd.

       Date:
           September 2012

       Definition at line 165 of file dlaqtr.f.

Author

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