c
c =====================================================
subroutine track(mx,q,x,xr,nc,fmin,fmax,dfmin)
c =====================================================
c
c Copyright (C) 2002 Ralf Deiterding
c Brandenburgische Universitaet Cottbus
c
c Copyright (C) 2003-2007 California Institute of Technology
c Ralf Deiterding, ralf@amroc.net
c
implicit double precision (a-h,o-z)
c
parameter ( mTab = 5000, mderiv = 2 )
common /Tables/ xtb(mderiv,-1:mTab), ftb(mderiv,-1:mTab)
c
dimension q(1:mx), x(1:mx), xr(1:mx)
c
nc = 0
do i=1,mx
xr(i) = -1.0d0
enddo
do i=1,mx-1
xtb(1,i) = 0.5d0*(x(i)+x(i+1))
ftb(1,i) = (q(i+1)-q(i))/(x(i+1)-x(i))
enddo
do i=1+1,mx-1
xtb(2,i) = 0.5d0*(xtb(1,i)+xtb(1,i-1))
ftb(2,i) = (ftb(1,i)-ftb(1,i-1))/(xtb(1,i)-xtb(1,i-1))
enddo
c
do i=1+2,mx-2
if (q(i).ge.fmin.and.q(i).le.fmax.and.
& dabs(ftb(1,i)*(x(i+1)-x(i))).gt.
& dfmin*(x(i+1)-x(i)).and.
& dsign(1.d0,ftb(2,i)).ne.
& dsign(1.d0,ftb(2,i+1))) then
c
nc = nc + 1
xr(nc) = xtb(2,i) + ftb(2,i)*(xtb(2,i+1)-xtb(2,i))/
& (ftb(2,i)-ftb(2,i+1))
endif
enddo
c
return
end
c