CLAQR1
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, CLAQR1 sets v to a
scalar multiple of the first column of the product
(*) K = (H - s1*I)*(H - s2*I)
scaling to avoid overflows and most underflows.
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) COMPLEX 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
S1 (input) COMPLEX
S2 S1 and S2 are the shifts defining K in (*) above.
V (output) COMPLEX 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, CLAQR1 sets v to a
scalar multiple of the first column of the product
(*) K = (H - s1*I)*(H - s2*I)
scaling to avoid overflows and most underflows.
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) COMPLEX 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
S1 (input) COMPLEX
S2 S1 and S2 are the shifts defining K in (*) above.
V (output) COMPLEX array of dimension N
A scalar multiple of the first column of the
matrix K in (*).