c
c
c     ###################################################
c     ##  COPYRIGHT (C)  1991  by  Jay William Ponder  ##
c     ##              All Rights Reserved              ##
c     ###################################################
c
c     ###########################################################
c     ##                                                       ##
c     ##  subroutine kimptor  --  improper torsion parameters  ##
c     ##                                                       ##
c     ###########################################################
c
c
c     "kimptor" assigns torsional parameters to each improper
c     torsion in the structure and processes any changed values
c
c
      subroutine kimptor
      implicit none
      include 'sizes.i'
      include 'atmtyp.i'
      include 'atoms.i'
      include 'couple.i'
      include 'imptor.i'
      include 'inform.i'
      include 'iounit.i'
      include 'keys.i'
      include 'kitors.i'
      include 'math.i'
      include 'potent.i'
      integer i,j,k,nti
      integer ia,ib,ic,id
      integer ita,itb,itc,itd
      integer size,next
      integer ft(6)
      real*8 angle,symm
      real*8 vt(6),st(6)
      logical header
      character*4 pa,pb,pc,pd
      character*16 blank,pti
      character*16 pt(6)
      character*20 keyword
      character*120 record
      character*120 string
c
c
c     process keywords containing improper 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(1:8) .eq. 'IMPTORS ') then
            ia = 0
            ib = 0
            ic = 0
            id = 0
            do j = 1, 6
               vt(j) = 0.0d0
               st(j) = 0.0d0
               ft(j) = 0
            end do
            string = record(next:120)
            read (string,*,err=10,end=10)  ia,ib,ic,id,
     &                                     (vt(j),st(j),ft(j),j=1,6)
   10       continue
            size = 4
            call numeral (ia,pa,size)
            call numeral (ib,pb,size)
            call numeral (ic,pc,size)
            call numeral (id,pd,size)
            pti = pa//pb//pc//pd
            call torphase (ft,vt,st)
            if (header) then
               header = .false.
               write (iout,20)
   20          format (/,' Additional Improper Torsion Parameters :',
     &                 //,5x,'Atom Classes',12x,'1-Fold',12x,'2-Fold',
     &                    12x,'3-Fold',/)
            end if
            write (iout,30)  ia,ib,ic,id,(vt(j),st(j),j=1,3)
   30       format (1x,4i4,2x,3(f11.4,f7.1))
            do j = 1, maxnti
               if (kti(j).eq.blank .or. kti(j).eq.pti) then
                  kti(j) = pti
                  ti1(1,j) = vt(1)
                  ti1(2,j) = st(1)
                  ti2(1,j) = vt(2)
                  ti2(2,j) = st(2)
                  ti3(1,j) = vt(3)
                  ti3(2,j) = st(3)
                  goto 50
               end if
            end do
            write (iout,40)
   40       format (/,' KIMPTOR  --  Too many Improper Torsion',
     &                 ' Parameters')
            abort = .true.
   50       continue
         end if
      end do
c
c     determine the total number of forcefield parameters
c
      nti = maxnti
      do i = maxnti, 1, -1
         if (kti(i) .eq. blank)  nti = i - 1
      end do
c
c     assign improper torsional parameters for each improper torsion;
c     multiple symmetrical parameters are given partial weights
c
      nitors = 0
      if (nti .ne. 0) then
         do i = 1, n
            if (n12(i) .eq. 3) then
               ia = i12(1,i)
               ib = i12(2,i)
               ic = i
               id = i12(3,i)
               ita = class(ia)
               itb = class(ib)
               itc = class(ic)
               itd = class(id)
               size = 4
               call numeral (ita,pa,size)
               call numeral (itb,pb,size)
               call numeral (itc,pc,size)
               call numeral (itd,pd,size)
               symm = 1.0d0
               if (pa.eq.pb .or. pa.eq.pd .or. pb.eq.pd)  symm = 2.0d0
               if (pa.eq.pb .and. pa.eq.pd .and. pb.eq.pd)  symm = 6.0d0
               do j = 1, nti
                  if (kti(j)(9:12) .eq. pc) then
                     pt(1) = pa//pb//pc//pd
                     pt(2) = pb//pa//pc//pd
                     pt(3) = pa//pd//pc//pb
                     pt(4) = pd//pa//pc//pb
                     pt(5) = pb//pd//pc//pa
                     pt(6) = pd//pb//pc//pa
                     do k = 1, 6
                        if (kti(j) .eq. pt(k)) then
                           nitors = nitors + 1
                           iitors(3,nitors) = ic
                           if (k .eq. 1) then
                              iitors(1,nitors) = ia
                              iitors(2,nitors) = ib
                              iitors(4,nitors) = id
                           else if (k .eq. 2) then
                              iitors(1,nitors) = ib
                              iitors(2,nitors) = ia
                              iitors(4,nitors) = id
                           else if (k .eq. 3) then
                              iitors(1,nitors) = ia
                              iitors(2,nitors) = id
                              iitors(4,nitors) = ib
                           else if (k .eq. 4) then
                              iitors(1,nitors) = id
                              iitors(2,nitors) = ia
                              iitors(4,nitors) = ib
                           else if (k .eq. 5) then
                              iitors(1,nitors) = ib
                              iitors(2,nitors) = id
                              iitors(4,nitors) = ia
                           else if (k .eq. 6) then
                              iitors(1,nitors) = id
                              iitors(2,nitors) = ib
                              iitors(4,nitors) = ia
                           end if
                           itors1(1,nitors) = ti1(1,j) / symm
                           itors1(2,nitors) = ti1(2,j)
                           itors2(1,nitors) = ti2(1,j) / symm
                           itors2(2,nitors) = ti2(2,j)
                           itors3(1,nitors) = ti3(1,j) / symm
                           itors3(2,nitors) = ti3(2,j)
                        end if
                     end do
                  end if
               end do
            end if
         end do
      end if
c
c     find the cosine and sine of the phase angle for each torsion
c
      do i = 1, nitors
         angle = itors1(2,i) / radian
         itors1(3,i) = cos(angle)
         itors1(4,i) = sin(angle)
         angle = itors2(2,i) / radian
         itors2(3,i) = cos(angle)
         itors2(4,i) = sin(angle)
         angle = itors3(2,i) / radian
         itors3(3,i) = cos(angle)
         itors3(4,i) = sin(angle)
      end do
c
c     turn off the improper torsional potential if it is not used
c
      if (nitors .eq. 0)  use_imptor = .false.
      return
      end
