# zlaqr1 (l) - Linux Man Pages

## SYNOPSIS

SUBROUTINE ZLAQR1(
N, H, LDH, S1, S2, V )

COMPLEX*16 S1, S2

INTEGER LDH, N

COMPLEX*16 H( LDH, * ), V( * )

COMPLEX*16 ZERO

PARAMETER ( ZERO = ( 0.0d0, 0.0d0 ) )

DOUBLE PRECISION RZERO

PARAMETER ( RZERO = 0.0d0 )

COMPLEX*16 CDUM, H21S, H31S

DOUBLE PRECISION S

INTRINSIC ABS, DBLE, DIMAG

DOUBLE PRECISION CABS1

CABS1( CDUM ) = ABS( DBLE( CDUM ) ) + ABS( DIMAG( CDUM ) )

IF( N.EQ.2 ) THEN

S = CABS1( H( 1, 1 )-S2 ) + CABS1( H( 2, 1 ) )

IF( S.EQ.RZERO ) THEN

V( 1 ) = ZERO

V( 2 ) = ZERO

ELSE

H21S = H( 2, 1 ) / S

V( 1 ) = H21S*H( 1, 2 ) + ( H( 1, 1 )-S1 )* ( ( H( 1, 1 )-S2 ) / S )

V( 2 ) = H21S*( H( 1, 1 )+H( 2, 2 )-S1-S2 )

END IF

ELSE

S = CABS1( H( 1, 1 )-S2 ) + CABS1( H( 2, 1 ) ) + CABS1( H( 3, 1 ) )

IF( S.EQ.ZERO ) THEN

V( 1 ) = ZERO

V( 2 ) = ZERO

V( 3 ) = ZERO

ELSE

H21S = H( 2, 1 ) / S

H31S = H( 3, 1 ) / S

V( 1 ) = ( H( 1, 1 )-S1 )*( ( H( 1, 1 )-S2 ) / S ) + H( 1, 2 )*H21S + H( 1, 3 )*H31S

V( 2 ) = H21S*( H( 1, 1 )+H( 2, 2 )-S1-S2 ) + H( 2, 3 )*H31S

V( 3 ) = H31S*( H( 1, 1 )+H( 3, 3 )-S1-S2 ) + H21S*H( 3, 2 )

END IF

END IF

END