subroutine interpolate_field(fringe_or_inflector,x,xgrid_point,B,b1,b2)
   use bmad
   use magfield
   use magfield_interface, dummy => interpolate_field
   use parameters_bmad
   implicit none
   real(rp) x(3), B(3),z, b1(3,3),b2(3,3)
   real(rp) xgrid(3), dx(3), xgrid_point(3)
   integer ind(3),i
   integer multiplier, fringe_or_inflector

   dx(1:3) = x(1:3) - xgrid_point(1:3) !distance from x to the nearest map grid point

!  print '(a,6es12.4)',' dx, B ', dx,B
   forall(i=1:3) B(i) = B(i) + dot_product(b1(i,:),dx(:))   ! B(i) =  grad(B(i)) . dx
!  print '(a,3es12.4)', 'B(1:3) ', B(1:3)
   return
  end subroutine