FIND_ROOT_POL.f90

Go to the documentation of this file.

!    Copyright (C) 2012 The SPEED FOUNDATION
!    Author: Ilario Mazzieri
!
!    This file is part of SPEED.
!
!    SPEED is free software; you can redistribute it and/or modify it
!    under the terms of the GNU Affero General Public License as
!    published by the Free Software Foundation, either version 3 of the
!    License, or (at your option) any later version.
!
!    SPEED is distributed in the hope that it will be useful, but
!    WITHOUT ANY WARRANTY; without even the implied warranty of
!    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
!    Affero General Public License for more details.
!
!    You should have received a copy of the GNU Affero General Public License
!    along with SPEED.  If not, see <http://www.gnu.org/licenses/>.
 
 
 
      real*8 function find_root_pol(x1,x2,xacc,n)
 
      use speed_exit_codes
      
      implicit real*8(a-h,o-z)
      
      parameter(jmax=1000)
      
      call get_legendre_value(p2,fmid,p1,p1der,n,x2)
      call get_legendre_value(p2,f,p1,p1der,n,x1)
 
      if (f*fmid .ge. 0.d0) then
        write(*,*) 'root non-bracketed !'
        call exit(exit_root)
      endif
      
      if (f .lt. 0.d0) then
        find_root_pol = x1
        dx = x2 - x1
      else
        find_root_pol = x2
        dx = x1 - x2
      endif
      
      do j = 1,jmax
        dx = 0.5d0*dx
        xmid = find_root_pol + dx
        call get_legendre_value(p2,fmid,p1,p1der,n,xmid)
        if (fmid .le. 0.d0) find_root_pol = xmid
        
        if (dabs(dx) .lt. xacc .and. dabs(fmid) .le. xacc) then
          find_root_pol = xmid
          return
        endif
        
      enddo
      
      end function find_root_pol