c
c
c     ###################################################
c     ##  COPYRIGHT (C)  2003  by  Jay William Ponder  ##
c     ##              All Rights Reserved              ##
c     ###################################################
c
c     ##################################################################
c     ##                                                              ##
c     ##  subroutine kpitors  --  find pi-orbital torsion parameters  ##
c     ##                                                              ##
c     ##################################################################
c
c
c     "kpitors" assigns pi-orbital torsion parameters to torsions
c     needing them, and processes any new or changed values
c
c
      subroutine kpitors
      implicit none
      include 'sizes.i'
      include 'atmtyp.i'
      include 'atoms.i'
      include 'bond.i'
      include 'couple.i'
      include 'inform.i'
      include 'iounit.i'
      include 'keys.i'
      include 'kpitor.i'
      include 'pitors.i'
      include 'potent.i'
      integer i,j,npt
      integer ia,ib
      integer ita,itb
      integer size,next
      real*8 tp
      logical header
      character*4 pa,pb
      character*8 blank,pt
      character*20 keyword
      character*120 record
      character*120 string
c
c
c     process keywords containing pi-orbital torsion parameters
c
      blank = '        '
      header = .true.
      do i = 1, nkey
         next = 1
         record = keyline(i)
         call gettext (record,keyword,next)
         call upcase (keyword)
         if (keyword(1:7) .eq. 'PITORS ') then
            ia = 0
            ib = 0
            tp = 0.0d0
            string = record(next:120)
            read (string,*,err=10,end=10)  ia,ib,tp
   10       continue
            if (header) then
               header = .false.
               write (iout,20)
   20          format (/,' Additional Pi-Orbital Torsion Parameters :',
     &                 //,5x,'Atom Classes',7x,'2-Fold',/)
            end if
            write (iout,30)  ia,ib,tp
   30       format (6x,2i4,4x,f12.3)
            size = 4
            call numeral (ia,pa,size)
            call numeral (ib,pb,size)
            if (ia .le. ib) then
               pt = pa//pb
            else
               pt = pb//pa
            end if
            do j = 1, maxnpt
               if (kpt(j).eq.blank .or. kpt(j).eq.pt) then
                  kpt(j) = pt
                  ptcon(j) = tp
                  goto 50
               end if
            end do
            write (iout,40)
   40       format (/,' KPITORS  --  Too many Pi-Orbital Torsion',
     &                 ' Parameters')
            abort = .true.
   50       continue
         end if
      end do
c
c     determine the total number of forcefield parameters
c
      npt = maxnpt
      do i = maxnpt, 1, -1
         if (kpt(i) .eq. blank)  npt = i - 1
      end do
c
c     assign pi-orbital torsion parameters as required
c
      npitors = 0
      if (npt .ne. 0) then
         do i = 1, nbond
            ia = ibnd(1,i)
            ib = ibnd(2,i)
            if (n12(ia).eq.3 .and. n12(ib).eq.3) then
               ita = class(ia)
               itb = class(ib)
               size = 4
               call numeral (ita,pa,size)
               call numeral (itb,pb,size)
               if (ita .le. itb) then
                  pt = pa//pb
               else
                  pt = pb//pa
               end if
               do j = 1, npt
                  if (kpt(j) .eq. pt) then
                     npitors = npitors + 1
                     kpit(npitors) = ptcon(j)
                     ipit(1,npitors) = i12(1,ia)
                     ipit(2,npitors) = i12(2,ia)
                     ipit(3,npitors) = ia
                     ipit(4,npitors) = ib
                     ipit(5,npitors) = i12(1,ib)
                     ipit(6,npitors) = i12(2,ib)
                     if (i12(1,ia) .eq. ib)
     &                  ipit(1,npitors) = i12(3,ia)
                     if (i12(2,ia) .eq. ib)
     &                  ipit(2,npitors) = i12(3,ia)
                     if (i12(1,ib) .eq. ia)
     &                  ipit(5,npitors) = i12(3,ib)
                     if (i12(2,ib) .eq. ia)
     &                  ipit(6,npitors) = i12(3,ib)
                     goto 60
                  end if
               end do
            end if
   60       continue
         end do
      end if
c
c     turn off the pi-orbital torsion potential if it is not used
c
c     if (npitors .eq. 0)  use_pitors = .false.
      return
      end