NAME

SRC/dlaqz2.f

SYNOPSIS

Functions/Subroutines

subroutine dlaqz2 (ilq, ilz, k, istartm, istopm, ihi, a, lda, b, ldb, nq, qstart, q, ldq, nz, zstart, z, ldz)
DLAQZ2

Function/Subroutine Documentation

subroutine dlaqz2 (logical, intent(in) ilq, logical, intent(in) ilz, integer, intent(in) k, integer, intent(in) istartm, integer, intent(in) istopm, integer, intent(in) ihi, double precision, dimension( lda, * ) a, integer, intent(in) lda, double precision, dimension( ldb, * ) b, integer, intent(in) ldb, integer, intent(in) nq, integer, intent(in) qstart, double precision, dimension( ldq, * ) q, integer, intent(in) ldq, integer, intent(in) nz, integer, intent(in) zstart, double precision, dimension( ldz, * ) z, integer, intent(in) ldz)

DLAQZ2

Purpose:



      DLAQZ2 chases a 2x2 shift bulge in a matrix pencil down a single position

Parameters

ILQ



          ILQ is LOGICAL


              Determines whether or not to update the matrix Q

ILZ



          ILZ is LOGICAL


              Determines whether or not to update the matrix Z



          K is INTEGER


              Index indicating the position of the bulge.


              On entry, the bulge is located in


              (A(k+1:k+2,k:k+1),B(k+1:k+2,k:k+1)).


              On exit, the bulge is located in


              (A(k+2:k+3,k+1:k+2),B(k+2:k+3,k+1:k+2)).

ISTARTM



          ISTARTM is INTEGER

ISTOPM



          ISTOPM is INTEGER


              Updates to (A,B) are restricted to


              (istartm:k+3,k:istopm). It is assumed


              without checking that istartm <= k+1 and


              k+2 <= istopm

IHI



          IHI is INTEGER



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

LDA



          LDA is INTEGER


              The leading dimension of A as declared in


              the calling procedure.



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

LDB



          LDB is INTEGER


              The leading dimension of B as declared in


              the calling procedure.



          NQ is INTEGER


              The order of the matrix Q

QSTART



          QSTART is INTEGER


              Start index of the matrix Q. Rotations are applied


              To columns k+2-qStart:k+4-qStart of Q.



          Q is DOUBLE PRECISION array, dimension (LDQ,NQ)

LDQ



          LDQ is INTEGER


              The leading dimension of Q as declared in


              the calling procedure.



          NZ is INTEGER


              The order of the matrix Z

ZSTART



          ZSTART is INTEGER


              Start index of the matrix Z. Rotations are applied


              To columns k+1-qStart:k+3-qStart of Z.



          Z is DOUBLE PRECISION array, dimension (LDZ,NZ)

LDZ



          LDZ is INTEGER


              The leading dimension of Q as declared in


              the calling procedure.

Author

Thijs Steel, KU Leuven

Date

May 2020

Definition at line 172 of file dlaqz2.f.

Author

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