LAPACK
3.6.1
LAPACK: Linear Algebra PACKage
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subroutine dlaqr1 | ( | integer | N, |
double precision, dimension( ldh, * ) | H, | ||
integer | LDH, | ||
double precision | SR1, | ||
double precision | SI1, | ||
double precision | SR2, | ||
double precision | SI2, | ||
double precision, dimension( * ) | V | ||
) |
DLAQR1 sets a scalar multiple of the first column of the product of 2-by-2 or 3-by-3 matrix H and specified shifts.
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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.
[in] | N | N is integer Order of the matrix H. N must be either 2 or 3. |
[in] | H | H is DOUBLE PRECISION array of dimension (LDH,N) The 2-by-2 or 3-by-3 matrix H in (*). |
[in] | LDH | LDH is integer The leading dimension of H as declared in the calling procedure. LDH.GE.N |
[in] | SR1 | SR1 is DOUBLE PRECISION |
[in] | SI1 | SI1 is DOUBLE PRECISION |
[in] | SR2 | SR2 is DOUBLE PRECISION |
[in] | SI2 | SI2 is DOUBLE PRECISION The shifts in (*). |
[out] | V | V is DOUBLE PRECISION array of dimension N A scalar multiple of the first column of the matrix K in (*). |
Definition at line 123 of file dlaqr1.f.