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c\BeginDoc
c
c\Name: cngets
c
c\Description:
c Given the eigenvalues of the upper Hessenberg matrix H,
c computes the NP shifts AMU that are zeros of the polynomial of
c degree NP which filters out components of the unwanted eigenvectors
c corresponding to the AMU's based on some given criteria.
c
c NOTE: call this even in the case of user specified shifts in order
c to sort the eigenvalues, and error bounds of H for later use.
c
c\Usage:
c call cngets
c ( ISHIFT, WHICH, KEV, NP, RITZ, BOUNDS )
c
c\Arguments
c ISHIFT Integer. (INPUT)
c Method for selecting the implicit shifts at each iteration.
c ISHIFT = 0: user specified shifts
c ISHIFT = 1: exact shift with respect to the matrix H.
c
c WHICH Character*2. (INPUT)
c Shift selection criteria.
c 'LM' -> want the KEV eigenvalues of largest magnitude.
c 'SM' -> want the KEV eigenvalues of smallest magnitude.
c 'LR' -> want the KEV eigenvalues of largest REAL part.
c 'SR' -> want the KEV eigenvalues of smallest REAL part.
c 'LI' -> want the KEV eigenvalues of largest imaginary part.
c 'SI' -> want the KEV eigenvalues of smallest imaginary part.
c
c KEV Integer. (INPUT)
c The number of desired eigenvalues.
c
c NP Integer. (INPUT)
c The number of shifts to compute.
c
c RITZ Complex array of length KEV+NP. (INPUT/OUTPUT)
c On INPUT, RITZ contains the the eigenvalues of H.
c On OUTPUT, RITZ are sorted so that the unwanted
c eigenvalues are in the first NP locations and the wanted
c portion is in the last KEV locations. When exact shifts are
c selected, the unwanted part corresponds to the shifts to
c be applied. Also, if ISHIFT .eq. 1, the unwanted eigenvalues
c are further sorted so that the ones with largest Ritz values
c are first.
c
c BOUNDS Complex array of length KEV+NP. (INPUT/OUTPUT)
c Error bounds corresponding to the ordering in RITZ.
c
c
c
c\EndDoc
c
c-----------------------------------------------------------------------
c
c\BeginLib
c
c\Local variables:
c xxxxxx Complex
c
c\Routines called:
c csortc ARPACK sorting routine.
c ivout ARPACK utility routine that prints integers.
c arscnd ARPACK utility routine for timing.
c cvout ARPACK utility routine that prints vectors.
c
c\Author
c Danny Sorensen Phuong Vu
c Richard Lehoucq CRPC / Rice University
c Dept. of Computational & Houston, Texas
c Applied Mathematics
c Rice University
c Houston, Texas
c
c\SCCS Information: @(#)
c FILE: ngets.F SID: 2.2 DATE OF SID: 4/20/96 RELEASE: 2
c
c\Remarks
c 1. This routine does not keep complex conjugate pairs of
c eigenvalues together.
c
c\EndLib
c
c-----------------------------------------------------------------------
c
subroutine cngets ( ishift, which, kev, np, ritz, bounds)
c
c %----------------------------------------------------%
c | Include files for debugging and timing information |
c %----------------------------------------------------%
c
include 'debug.h'
include 'stat.h'
c
c %------------------%
c | Scalar Arguments |
c %------------------%
c
character*2 which
integer ishift, kev, np
c
c %-----------------%
c | Array Arguments |
c %-----------------%
c
Complex
& bounds(kev+np), ritz(kev+np)
c
c %------------%
c | Parameters |
c %------------%
c
Complex
& one, zero
parameter (one = (1.0E+0, 0.0E+0), zero = (0.0E+0, 0.0E+0))
c
c %---------------%
c | Local Scalars |
c %---------------%
c
integer msglvl
c
c %----------------------%
c | External Subroutines |
c %----------------------%
c
external cvout, csortc, arscnd
c
c %-----------------------%
c | Executable Statements |
c %-----------------------%
c
c %-------------------------------%
c | Initialize timing statistics |
c | & message level for debugging |
c %-------------------------------%
c
call arscnd (t0)
msglvl = mcgets
c
call csortc (which, .true., kev+np, ritz, bounds)
c
if ( ishift .eq. 1 ) then
c
c %-------------------------------------------------------%
c | Sort the unwanted Ritz values used as shifts so that |
c | the ones with largest Ritz estimates are first |
c | This will tend to minimize the effects of the |
c | forward instability of the iteration when the shifts |
c | are applied in subroutine cnapps. |
c | Be careful and use 'SM' since we want to sort BOUNDS! |
c %-------------------------------------------------------%
c
call csortc ( 'SM', .true., np, bounds, ritz )
c
end if
c
call arscnd (t1)
tcgets = tcgets + (t1 - t0)
c
if (msglvl .gt. 0) then
call ivout (logfil, 1, kev, ndigit, '_ngets: KEV is')
call ivout (logfil, 1, np, ndigit, '_ngets: NP is')
call cvout (logfil, kev+np, ritz, ndigit,
& '_ngets: Eigenvalues of current H matrix ')
call cvout (logfil, kev+np, bounds, ndigit,
& '_ngets: Ritz estimates of the current KEV+NP Ritz values')
end if
c
return
c
c %---------------%
c | End of cngets |
c %---------------%
c
end
|
