c ***********************************************************************

      subroutine relativeorientation(n,i1,i2,cos1,cos2)
c calculate the relative orientation through cos1, cos2
      implicit double precision(a-h, o-z)
      parameter(maxa=500,maxn=maxa*3)
      double precision d(3),d1(3),d2(3),lengthd1,lengthd2
       common/matrix/x(maxa,3),bangle(maxa),rz(maxa)
       common/matrix2/ r(maxa,maxa)
       common/bf_coords/f(maxa,3),v(maxa,3),u(maxa,3)
 
       do j=1,3
          d(j)=x(i2,j)-x(i1,j)
       enddo

       du1=0
       du2=0
       cos1=0
       cos2=0
       lengthd1=0
       lengthd2=0

       do j=1,3
          du1=d(j)*u(i1,j)+du1
          du2=d(j)*u(i2,j)+du2
       enddo

       do j=1,3
          d1(j)=d(j)-du1*u(i1,j)
          d2(j)=d(j)-du2*u(i2,j)
          lengthd1=lengthd1+d1(j)*d1(j)
          lengthd2=lengthd2+d2(j)*d2(j)         
       enddo

       do j=1,3
          cos1=cos1+f(i1,j)*d(j)
          cos2=cos2+f(i2,j)*d(j)
       enddo
       
       cos1=cos1/dsqrt(lengthd1)
       cos2=cos2/dsqrt(lengthd2)
       
       return
       end