subroutine claqr1 (N, H, LDH, S1, S2, V)
CLAQR1 sets a scalar multiple of the first column of the product of 2-by-2 or 3-by-3 matrix H and specified shifts.
CLAQR1 sets a scalar multiple of the first column of the product of 2-by-2 or 3-by-3 matrix H and specified shifts.
Purpose:
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.
Parameters:
N is INTEGER Order of the matrix H. N must be either 2 or 3.
H
H is COMPLEX array, dimension (LDH,N) The 2-by-2 or 3-by-3 matrix H in (*).
LDH
LDH is INTEGER The leading dimension of H as declared in the calling procedure. LDH.GE.N
S1
S1 is COMPLEX
S2
S2 is COMPLEX S1 and S2 are the shifts defining K in (*) above.
V
V is COMPLEX array, dimension (N) A scalar multiple of the first column of the matrix K in (*).
Author:
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date:
Contributors:
Definition at line 109 of file claqr1.f.
Generated automatically by Doxygen for LAPACK from the source code.