[数值问题] NAN求助

      program pxrd
      implicit none
      real(4),parameter::natom=143,n=180,lambda=1.5406,frame=1000
      integer::i,j,k,l
      real(4),dimension(natom,n)::f
      real(4),dimension(natom,natom)::r
      character::u
      real(4),parameter::pi=4.d0*datan(1.d0)
      real(8)::intensity0,intensity1,intensity2,intensity,s
      open(11,file='facter.txt')
      open(12,file='pbc.txt')
      open(13,file='pxrd.txt')
      open(14,file='ceshi.txt')     
      do i=1,natom
        read(11,*)f(i,1:n)
      enddo
      
c      do l=1,frame
        do i=1,natom
          read(12,*)r(i,1:natom)
        enddo
        do i=1,n
          intensity1=0.d0
          intensity2=0.d0
          s=4*pi/lambda*(sin(n*pi/180))
          do j=1,natom
            do k=1,natom
              if(j.ne.k) then
                intensity1=intensity1+(f(j,i)*f(k,i)*
     x                   (sin(s*r(j,k))/s/r(j,k)))
              else
                intensity2=intensity2+(f(j,i)*f(k,i))
              endif
              write(14,*)intensity1,intensity2
            enddo
          enddo
            intensity=intensity1+intensity2
            write(13,*)intensity
        enddo
c      enddo
      close(11)
      close(12)
      close(13)
      close(14)
      end