*************************************************************************
*     
*     Subroutine inter_B.f (from tracker software analysis)
*     
*     it computes the magnetic field in a chosen point x,y,z inside or 
*     outside the magnetic cavity, using a trilinear interpolation of
*     B field measurements (read before by means of ./read_B.f)
*     if the point falls outside the interpolation volume, set the field to 0
*     
*     needs:
*     - ../common/common_B_inner.f common file for the inner magnetic field map
*     - ./inter_B_inner.f common file for the inner magnetic field map
*     
*     to be called after ./read_B.f (magnetic field map reading subroutine)
*     
*     input: coordinates in m
*     output: magnetic field in T
*     
*************************************************************************

      subroutine inter_B(x,y,z,res) !coordinates in m, magnetic field in T
      IMPLICIT DOUBLE PRECISION (A-H,O-Z)
#include "gpfield.inc"

c------------------------------------------------------------------------
c     
c     local variables
c     
c------------------------------------------------------------------------

      real*8 x,y,z              !point of interest
      real*8 res(3)             !interpolated B components: res = (Bx, By, Bz)


c------------------------------------------------------------------------
c     
c     set the field outside the interpolation volume to be 0
c     
c------------------------------------------------------------------------

      do ip=1,3
        res(ip)=0.
      enddo


c------------------------------------------------------------------------
c     
c     check if the point falls inside the interpolation volume
c     
c------------------------------------------------------------------------
      
      if((x.ge.edgexmin).and.(x.le.edgexmax)
     $     .and.(y.ge.edgeymin).and.(y.le.edgeymax)
     $     .and.(z.ge.edgezmin).and.(z.le.edgezmax)) then

        call inter_B_inner(x,y,z,res)
       
      endif

c     TODO: add inter_B_outer subroutine(s) for the external magnetic field map

      return
      end