DLAQR1
Univ. of Tennessee, Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..
November 2006
Given a 2-by-2 or 3-by-3 matrix H, DLAQR1 sets v to a
scalar multiple of the first column of the product
(*) K = (H - (sr1 + i*si1)*I)*(H - (sr2 + i*si2)*I)
scaling to avoid overflows and most underflows. It
is assumed that either
1) sr1 = sr2 and si1 = -si2
or
2) si1 = si2 = 0.
This is useful for starting double implicit shift bulges
in the QR algorithm.
N (input) integer
Order of the matrix H. N must be either 2 or 3.
H (input) DOUBLE PRECISION array of dimension (LDH,N)
The 2-by-2 or 3-by-3 matrix H in (*).
LDH (input) integer
The leading dimension of H as declared in
the calling procedure. LDH.GE.N
SR1 (input) DOUBLE PRECISION
SI1 The shifts in (*).
SR2
SI2
V (output) DOUBLE PRECISION array of dimension N
A scalar multiple of the first column of the
matrix K in (*).
November 2006
Given a 2-by-2 or 3-by-3 matrix H, DLAQR1 sets v to a
scalar multiple of the first column of the product
(*) K = (H - (sr1 + i*si1)*I)*(H - (sr2 + i*si2)*I)
scaling to avoid overflows and most underflows. It
is assumed that either
1) sr1 = sr2 and si1 = -si2
or
2) si1 = si2 = 0.
This is useful for starting double implicit shift bulges
in the QR algorithm.
N (input) integer
Order of the matrix H. N must be either 2 or 3.
H (input) DOUBLE PRECISION array of dimension (LDH,N)
The 2-by-2 or 3-by-3 matrix H in (*).
LDH (input) integer
The leading dimension of H as declared in
the calling procedure. LDH.GE.N
SR1 (input) DOUBLE PRECISION
SI1 The shifts in (*).
SR2
SI2
V (output) DOUBLE PRECISION array of dimension N
A scalar multiple of the first column of the
matrix K in (*).