slaqtr.f File Reference

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

---

Function/Subroutine Documentation

subroutine slaqtr	(	logical	LTRAN,
		logical	LREAL,
		integer	N,
		real, dimension( ldt, * )	T,
		integer	LDT,
		real, dimension( * )	B,
		real	W,
		real	SCALE,
		real, dimension( * )	X,
		real, dimension( * )	WORK,
		integer	INFO
	)

SLAQTR solves a real quasi-triangular system of equations, or a complex quasi-triangular system of special form, in real arithmetic.

Download SLAQTR + dependencies [TGZ] [ZIP] [TXT]

Purpose:

 SLAQTR 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 STRSNA.

Parameters:

[in]	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.
[in]	LREAL	LREAL is LOGICAL On entry, LREAL specifies the input matrix structure: = .FALSE., the input is complex = .TRUE., the input is real
[in]	N	N is INTEGER On entry, N specifies the order of T+i*B. N >= 0.
[in]	T	T is REAL array, dimension (LDT,N) On entry, T contains a matrix in Schur canonical form. If LREAL = .FALSE., then the first diagonal block of T must be 1 by 1.
[in]	LDT	LDT is INTEGER The leading dimension of the matrix T. LDT >= max(1,N).
[in]	B	B is REAL array, dimension (N) On entry, B contains the elements to form the matrix B as described above. If LREAL = .TRUE., B is not referenced.
[in]	W	W is REAL On entry, W is the diagonal element of the matrix B. If LREAL = .TRUE., W is not referenced.
[out]	SCALE	SCALE is REAL On exit, SCALE is the scale factor.
[in,out]	X	X is REAL array, dimension (2*N) On entry, X contains the right hand side of the system. On exit, X is overwritten by the solution.
[out]	WORK	WORK is REAL array, dimension (N)
[out]	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 SLALN2 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 slaqtr.f.

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