.TH "SRC/dlaqr1.f" 3 "Version 3.12.0" "LAPACK" \" -*- nroff -*- .ad l .nh .SH NAME SRC/dlaqr1.f .SH SYNOPSIS .br .PP .SS "Functions/Subroutines" .in +1c .ti -1c .RI "subroutine \fBdlaqr1\fP (n, h, ldh, sr1, si1, sr2, si2, v)" .br .RI "\fBDLAQR1\fP sets a scalar multiple of the first column of the product of 2-by-2 or 3-by-3 matrix H and specified shifts\&. " .in -1c .SH "Function/Subroutine Documentation" .PP .SS "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)" .PP \fBDLAQR1\fP sets a scalar multiple of the first column of the product of 2-by-2 or 3-by-3 matrix H and specified shifts\&. .PP \fBPurpose:\fP .RS 4 .PP .nf 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\&. .fi .PP .RE .PP \fBParameters\fP .RS 4 \fIN\fP .PP .nf N is INTEGER Order of the matrix H\&. N must be either 2 or 3\&. .fi .PP .br \fIH\fP .PP .nf H is DOUBLE PRECISION array, dimension (LDH,N) The 2-by-2 or 3-by-3 matrix H in (*)\&. .fi .PP .br \fILDH\fP .PP .nf LDH is INTEGER The leading dimension of H as declared in the calling procedure\&. LDH >= N .fi .PP .br \fISR1\fP .PP .nf SR1 is DOUBLE PRECISION .fi .PP .br \fISI1\fP .PP .nf SI1 is DOUBLE PRECISION .fi .PP .br \fISR2\fP .PP .nf SR2 is DOUBLE PRECISION .fi .PP .br \fISI2\fP .PP .nf SI2 is DOUBLE PRECISION The shifts in (*)\&. .fi .PP .br \fIV\fP .PP .nf V is DOUBLE PRECISION array, dimension (N) A scalar multiple of the first column of the matrix K in (*)\&. .fi .PP .RE .PP \fBAuthor\fP .RS 4 Univ\&. of Tennessee .PP Univ\&. of California Berkeley .PP Univ\&. of Colorado Denver .PP NAG Ltd\&. .RE .PP \fBContributors:\fP .RS 4 Karen Braman and Ralph Byers, Department of Mathematics, University of Kansas, USA .RE .PP .PP Definition at line \fB120\fP of file \fBdlaqr1\&.f\fP\&. .SH "Author" .PP Generated automatically by Doxygen for LAPACK from the source code\&.