slaqtr.f(3) LAPACK slaqtr.f(3)
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.
subroutine slaqtr (logicalLTRAN, logicalLREAL, integerN, real, dimension( ldt, * )T,
integerLDT, real, dimension( * )B, realW, realSCALE, real, dimension( * )X, real,
dimension( * )WORK, integerINFO)
SLAQTR solves a real quasi-triangular system of equations, or a complex quasi-triangular
system of special form, in real arithmetic.
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
On input, X = [ c ]. On output, X = [ p ].
[ d ] [ q ]
This subroutine is designed for the condition number estimation
in routine STRSNA.
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 is LOGICAL
On entry, LREAL specifies the input matrix structure:
= .FALSE., the input is complex
= .TRUE., the input is real
N is INTEGER
On entry, N specifies the order of T+i*B. N >= 0.
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.
LDT is INTEGER
The leading dimension of the matrix T. LDT >= max(1,N).
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.
W is REAL
On entry, W is the diagonal element of the matrix B.
If LREAL = .TRUE., W is not referenced.
SCALE is REAL
On exit, SCALE is the scale factor.
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.
WORK is REAL array, dimension (N)
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.
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
Definition at line 165 of file slaqtr.f.
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Version 3.4.2 Tue Sep 25 2012 slaqtr.f(3)