NAME

SRC/dlaqz1.f

SYNOPSIS

Functions/Subroutines

subroutine dlaqz1 (a, lda, b, ldb, sr1, sr2, si, beta1, beta2, v)
DLAQZ1

Function/Subroutine Documentation

subroutine dlaqz1 (double precision, dimension( lda, * ), intent(in) a, integer, intent(in) lda, double precision, dimension( ldb, * ), intent(in) b, integer, intent(in) ldb, double precision, intent(in) sr1, double precision, intent(in) sr2, double precision, intent(in) si, double precision, intent(in) beta1, double precision, intent(in) beta2, double precision, dimension( * ), intent(out) v)

DLAQZ1

Purpose:



      Given a 3-by-3 matrix pencil (A,B), DLAQZ1 sets v to a


      scalar multiple of the first column of the product


      (*)  K = (A - (beta2*sr2 - i*si)*B)*B^(-1)*(beta1*A - (sr2 + i*si2)*B)*B^(-1).


      It is assumed that either


              1) sr1 = sr2


          or


              2) si = 0.


      This is useful for starting double implicit shift bulges


      in the QZ algorithm.

Parameters



          A is DOUBLE PRECISION array, dimension (LDA,N)


              The 3-by-3 matrix A in (*).

LDA



          LDA is INTEGER


              The leading dimension of A as declared in


              the calling procedure.



          B is DOUBLE PRECISION array, dimension (LDB,N)


              The 3-by-3 matrix B in (*).

LDB



          LDB is INTEGER


              The leading dimension of B as declared in


              the calling procedure.

SR1



          SR1 is DOUBLE PRECISION

SR2



          SR2 is DOUBLE PRECISION



          SI is DOUBLE PRECISION

BETA1



          BETA1 is DOUBLE PRECISION

BETA2



          BETA2 is DOUBLE PRECISION



          V is DOUBLE PRECISION array, dimension (N)


              A scalar multiple of the first column of the


              matrix K in (*).

Author

Thijs Steel, KU Leuven

Date

May 2020

Definition at line 125 of file dlaqz1.f.

Author

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