CoCalc -- dsconv.f

GitHub Repository: ElmerCSC/elmerfem
Path: blob/devel/mathlibs/src/arpack/dsconv.f
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c-----------------------------------------------------------------------
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c\BeginDoc
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c
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c\Name: dsconv
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c
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c\Description: 
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c  Convergence testing for the symmetric Arnoldi eigenvalue routine.
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c
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c\Usage:
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c  call dsconv
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c     ( N, RITZ, BOUNDS, TOL, NCONV )
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c
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c\Arguments
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c  N       Integer.  (INPUT)
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c          Number of Ritz values to check for convergence.
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c
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c  RITZ    Double precision array of length N.  (INPUT)
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c          The Ritz values to be checked for convergence.
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c
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c  BOUNDS  Double precision array of length N.  (INPUT)
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c          Ritz estimates associated with the Ritz values in RITZ.
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c
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c  TOL     Double precision scalar.  (INPUT)
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c          Desired relative accuracy for a Ritz value to be considered
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c          "converged".
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c
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c  NCONV   Integer scalar.  (OUTPUT)
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c          Number of "converged" Ritz values.
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c
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c\EndDoc
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c
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c-----------------------------------------------------------------------
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c
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c\BeginLib
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c
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c\Routines called:
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c     second  ARPACK utility routine for timing.
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c     dlamch  LAPACK routine that determines machine constants. 
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c
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c\Author
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c     Danny Sorensen               Phuong Vu
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c     Richard Lehoucq              CRPC / Rice University 
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c     Dept. of Computational &     Houston, Texas 
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c     Applied Mathematics
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c     Rice University           
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c     Houston, Texas            
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c
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c\SCCS Information: @(#) 
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c FILE: sconv.F   SID: 2.4   DATE OF SID: 4/19/96   RELEASE: 2
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c
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c\Remarks
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c     1. Starting with version 2.4, this routine no longer uses the
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c        Parlett strategy using the gap conditions. 
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c
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c\EndLib
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c
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c-----------------------------------------------------------------------
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c
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      subroutine dsconv (n, ritz, bounds, tol, nconv)
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c
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c     %----------------------------------------------------%
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c     | Include files for debugging and timing information |
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c     %----------------------------------------------------%
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c
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      include   'debug.h'
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      include   'stat.h'
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c
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c     %------------------%
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c     | Scalar Arguments |
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c     %------------------%
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c
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      integer    n, nconv
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      Double precision
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     &           tol
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c
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c     %-----------------%
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c     | Array Arguments |
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c     %-----------------%
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c
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      Double precision
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     &           ritz(n), bounds(n)
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c
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c     %---------------%
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c     | Local Scalars |
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c     %---------------%
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c
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      integer    i
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      Double precision
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     &           temp, eps23
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c
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c     %-------------------%
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c     | External routines |
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c     %-------------------%
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c
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      Double precision
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     &           dlamch
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      external   dlamch
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c     %---------------------%
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c     | Intrinsic Functions |
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c     %---------------------%
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c
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      intrinsic    abs
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c
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c     %-----------------------%
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c     | Executable Statements |
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c     %-----------------------%
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c
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      call second (t0)
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c
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      eps23 = dlamch('Epsilon-Machine') 
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      eps23 = eps23**(2.0D+0 / 3.0D+0)
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c
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      nconv  = 0
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      do 10 i = 1, n
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c
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c        %-----------------------------------------------------%
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c        | The i-th Ritz value is considered "converged"       |
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c        | when: bounds(i) .le. TOL*max(eps23, abs(ritz(i)))   |
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c        %-----------------------------------------------------%
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c
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         temp = max( eps23, abs(ritz(i)) )
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         if ( bounds(i) .le. tol*temp ) then
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            nconv = nconv + 1
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         end if
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c
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   10 continue
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c 
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      call second (t1)
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      tsconv = tsconv + (t1 - t0)
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c 
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      return
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c
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c     %---------------%
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c     | End of dsconv |
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c     %---------------%
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c
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      end
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