c-----------------------------------------------------------------------
c\BeginDoc
c
c\Name: dngets
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 dngets
c ( ISHIFT, WHICH, KEV, NP, RITZR, RITZI, BOUNDS, SHIFTR, SHIFTI )
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/OUTPUT)
c INPUT: KEV+NP is the size of the matrix H.
c OUTPUT: Possibly increases KEV by one to keep complex conjugate
c pairs together.
c
c NP Integer. (INPUT/OUTPUT)
c Number of implicit shifts to be computed.
c OUTPUT: Possibly decreases NP by one to keep complex conjugate
c pairs together.
c
c RITZR, Double precision array of length KEV+NP. (INPUT/OUTPUT)
c RITZI On INPUT, RITZR and RITZI contain the real and imaginary
c parts of the eigenvalues of H.
c On OUTPUT, RITZR and RITZI 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 Double precision array of length KEV+NP. (INPUT/OUTPUT)
c Error bounds corresponding to the ordering in RITZ.
c
c SHIFTR, SHIFTI *** USE deprecated as of version 2.1. ***
c
c
c\EndDoc
c
c-----------------------------------------------------------------------
c
c\BeginLib
c
c\Local variables:
c xxxxxx real
c
c\Routines called:
c dsortc ARPACK sorting routine.
c dcopy Level 1 BLAS that copies one vector to another .
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\Revision history:
c xx/xx/92: Version ' 2.1'
c
c\SCCS Information: @(#)
c FILE: ngets.F SID: 2.3 DATE OF SID: 4/20/96 RELEASE: 2
c
c\Remarks
c 1. xxxx
c
c\EndLib
c
c-----------------------------------------------------------------------
c
subroutine dngets ( ishift, which, kev, np, ritzr, ritzi, bounds,
& shiftr, shifti )
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
Double precision
& bounds(kev+np), ritzr(kev+np), ritzi(kev+np),
& shiftr(1), shifti(1)
c
c %------------%
c | Parameters |
c %------------%
c
Double precision
& one, zero
parameter (one = 1.0, zero = 0.0)
c
c %---------------%
c | Local Scalars |
c %---------------%
c
integer msglvl
c
c %----------------------%
c | External Subroutines |
c %----------------------%
c
external dcopy, dsortc, second
c
c %----------------------%
c | Intrinsics Functions |
c %----------------------%
c
intrinsic abs
c
c %-----------------------%
c | Executable Statements |
c %-----------------------%
c
c %-------------------------------%
c | Initialize timing statistics |
c | & message level for debugging |
c %-------------------------------%
c
call second (t0)
msglvl = mngets
c
c %----------------------------------------------------%
c | LM, SM, LR, SR, LI, SI case. |
c | Sort the eigenvalues of H into the desired order |
c | and apply the resulting order to BOUNDS. |
c | The eigenvalues are sorted so that the wanted part |
c | are always in the last KEV locations. |
c | We first do a pre-processing sort in order to keep |
c | complex conjugate pairs together |
c %----------------------------------------------------%
c
if (which .eq. 'LM') then
call dsortc ('LR', .true., kev+np, ritzr, ritzi, bounds)
else if (which .eq. 'SM') then
call dsortc ('SR', .true., kev+np, ritzr, ritzi, bounds)
else if (which .eq. 'LR') then
call dsortc ('LM', .true., kev+np, ritzr, ritzi, bounds)
else if (which .eq. 'SR') then
call dsortc ('SM', .true., kev+np, ritzr, ritzi, bounds)
else if (which .eq. 'LI') then
call dsortc ('LM', .true., kev+np, ritzr, ritzi, bounds)
else if (which .eq. 'SI') then
call dsortc ('SM', .true., kev+np, ritzr, ritzi, bounds)
end if
c
call dsortc (which, .true., kev+np, ritzr, ritzi, bounds)
c
c %-------------------------------------------------------%
c | Increase KEV by one if the ( ritzr(np),ritzi(np) ) |
c | = ( ritzr(np+1),-ritzi(np+1) ) and ritz(np) .ne. zero |
c | Accordingly decrease NP by one. In other words keep |
c | complex conjugate pairs together. |
c %-------------------------------------------------------%
c
if ( ( ritzr(np+1) - ritzr(np) ) .eq. zero
& .and. ( ritzi(np+1) + ritzi(np) ) .eq. zero ) then
np = np - 1
kev = kev + 1
end if
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 they shifts |
c | are applied in subroutine dnapps. |
c | Be careful and use 'SR' since we want to sort BOUNDS
c %-------------------------------------------------------%
c
call dsortc ( 'SR', .true., np, bounds, ritzr, ritzi )
end if
c
call second (t1)
tngets = tngets + (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 dvout (logfil, kev+np, ritzr, ndigit,
& '_ngets: Eigenvalues of current H matrix -- real part')
call dvout (logfil, kev+np, ritzi, ndigit,
& '_ngets: Eigenvalues of current H matrix -- imag part')
call dvout (logfil, kev+np, bounds, ndigit,
& '_ngets: Ritz estimates of the current KEV+NP Ritz values')
end if
c
return
c
c %---------------%
c | End of dngets |
c %---------------%
c
end
