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slaqr1.f(3) LAPACK slaqr1.f(3)

NAME

slaqr1.f -

SYNOPSIS

Functions/Subroutines


subroutine slaqr1 (N, H, LDH, SR1, SI1, SR2, SI2, V)
 
SLAQR1 sets a scalar multiple of the first column of the product of 2-by-2 or 3-by-3 matrix H and specified shifts.

Function/Subroutine Documentation

subroutine slaqr1 (integerN, real, dimension( ldh, * )H, integerLDH, realSR1, realSI1, realSR2, realSI2, real, dimension( * )V)

SLAQR1 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, SLAQR1 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.
Parameters:
N 
          N is integer
              Order of the matrix H. N must be either 2 or 3.
H 
          H is REAL array of 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
SR1 
          SR1 is REAL
SI1 
          SI1 is REAL
SR2 
          SR2 is REAL
SI2 
          SI2 is REAL
              The shifts in (*).
V 
          V is REAL array of dimension N
              A scalar multiple of the first column of the
              matrix K in (*).
Author:
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date:
September 2012
Contributors:
Karen Braman and Ralph Byers, Department of Mathematics, University of Kansas, USA
Definition at line 122 of file slaqr1.f.

Author

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