dlaed6 (l)  Linux Man Pages
dlaed6: computes the positive or negative root (closest to the origin) of z(1) z(2) z(3) f(x) = rho +  +  +  d(1)x d(2)x d(3)x It is assumed that if ORGATI = .true
NAME
DLAED6  computes the positive or negative root (closest to the origin) of z(1) z(2) z(3) f(x) = rho +  +  +  d(1)x d(2)x d(3)x It is assumed that if ORGATI = .trueSYNOPSIS
 SUBROUTINE DLAED6(
 KNITER, ORGATI, RHO, D, Z, FINIT, TAU, INFO )
 LOGICAL ORGATI
 INTEGER INFO, KNITER
 DOUBLE PRECISION FINIT, RHO, TAU
 DOUBLE PRECISION D( 3 ), Z( 3 )
PURPOSE
DLAED6 computes the positive or negative root (closest to the origin) ofotherwise it is between
This routine will be called by DLAED4 when necessary. In most cases, the root sought is the smallest in magnitude, though it might not be in some extremely rare situations.
ARGUMENTS
 KNITER (input) INTEGER
 Refer to DLAED4 for its significance.
 ORGATI (input) LOGICAL
 If ORGATI is true, the needed root is between d(2) and d(3); otherwise it is between d(1) and d(2). See DLAED4 for further details.
 RHO (input) DOUBLE PRECISION
 Refer to the equation f(x) above.
 D (input) DOUBLE PRECISION array, dimension (3)
 D satisfies d(1) < d(2) < d(3).
 Z (input) DOUBLE PRECISION array, dimension (3)
 Each of the elements in z must be positive.
 FINIT (input) DOUBLE PRECISION
 The value of f at 0. It is more accurate than the one evaluated inside this routine (if someone wants to do so).
 TAU (output) DOUBLE PRECISION
 The root of the equation f(x).
 INFO (output) INTEGER

= 0: successful exit
> 0: if INFO = 1, failure to converge
FURTHER DETAILS
30/06/99: Based on contributions byRenCang Li, Computer Science Division, University of California
at Berkeley, USA
10/02/03: This version has a few statements commented out for thread safety (machine parameters are computed on each entry). SJH. 05/10/06: Modified from a new version of RenCang Li, use
GraggThorntonWarner cubic convergent scheme for better stability.