dlaqtr (l)  Linux Man Pages
dlaqtr: solves the real quasitriangular system op(T)*p = scale*c, if LREAL = .TRUE
NAME
DLAQTR  solves the real quasitriangular system op(T)*p = scale*c, if LREAL = .TRUESYNOPSIS
 SUBROUTINE DLAQTR(
 LTRAN, LREAL, N, T, LDT, B, W, SCALE, X, WORK, INFO )
 LOGICAL LREAL, LTRAN
 INTEGER INFO, LDT, N
 DOUBLE PRECISION SCALE, W
 DOUBLE PRECISION B( * ), T( LDT, * ), WORK( * ), X( * )
PURPOSE
DLAQTR solves the real quasitriangular system or the complex quasitriangular systemsIf LREAL = .FALSE., then the first diagonal block of T must be 1 by 1, B is the specially structured matrix
op(A) = A or Aaq, Aaq denotes the conjugate transpose of
matrix A.
On input, X = [ c ]. On output, X = [ p ].
This subroutine is designed for the condition number estimation in routine DTRSNA.
ARGUMENTS
 LTRAN (input) 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)aq.
 LREAL (input) LOGICAL
 On entry, LREAL specifies the input matrix structure: = .FALSE., the input is complex = .TRUE., the input is real
 N (input) INTEGER
 On entry, N specifies the order of T+i*B. N >= 0.
 T (input) 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 (input) INTEGER
 The leading dimension of the matrix T. LDT >= max(1,N).
 B (input) 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 (input) DOUBLE PRECISION
 On entry, W is the diagonal element of the matrix B. If LREAL = .TRUE., W is not referenced.
 SCALE (output) DOUBLE PRECISION
 On exit, SCALE is the scale factor.
 X (input/output) 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 (workspace) DOUBLE PRECISION array, dimension (N)
 INFO (output) 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.