!------------------------------------------------------------------
!
!   calculate distance between two cartesian points
!
!-----------------------------------------------------------------

          real function distance(x1,y1,z1,x2,y2,z2)

            implicit none

            real,intent(in)::x1,y1,z1,x2,y2,z2

            distance=sqrt((x1-x2)**2+(y1-y2)**2+(z1-z2)**2)

          end function distance