dlaqr1 man page on Scientific
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DLAQR1(1) LAPACK auxiliary routine (version 3.2) DLAQR1(1)
NAME
SYNOPSIS
SUBROUTINE DLAQR1( N, H, LDH, SR1, SI1, SR2, SI2, V )
DOUBLE PRECISION SI1, SI2, SR1, SR2
INTEGER LDH, N
DOUBLE PRECISION H( LDH, * ), V( * )
DOUBLE PRECISION ZERO
PARAMETER ( ZERO = 0.0d0 )
DOUBLE PRECISION H21S, H31S, S
INTRINSIC ABS
IF( N.EQ.2 ) THEN
S = ABS( H( 1, 1 )-SR2 ) + ABS( SI2 ) + ABS( H( 2, 1 )
)
IF( S.EQ.ZERO ) THEN
V( 1 ) = ZERO
V( 2 ) = ZERO
ELSE
H21S = H( 2, 1 ) / S
V( 1 ) = H21S*H( 1, 2 ) + ( H( 1, 1 )-SR1 )* ( ( H( 1,
1 )-SR2 ) / S ) - SI1*( SI2 / S )
V( 2 ) = H21S*( H( 1, 1 )+H( 2, 2 )-SR1-SR2 )
END IF
ELSE
S = ABS( H( 1, 1 )-SR2 ) + ABS( SI2 ) + ABS( H( 2, 1 )
) + ABS( 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 )-SR1 )*( ( H( 1, 1 )-SR2 ) / S ) -
SI1*( SI2 / S ) + H( 1, 2 )*H21S + H( 1, 3 )*H31S
V( 2 ) = H21S*( H( 1, 1 )+H( 2, 2 )-SR1-SR2 ) + H( 2, 3
)*H31S
V( 3 ) = H31S*( H( 1, 1 )+H( 3, 3 )-SR1-SR2 ) + H21S*H(
3, 2 )
END IF
END IF
END
PURPOSE
LAPACK auxiliary routine (versioNovember 2008 DLAQR1(1)
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