anchor.diff:     ErrStat = ErrID_None
      ErrMsg  = ""
      
  -   ! initialize accelerations here:
  -   if ( .not. OtherState%InitAcc) then
  -      !Qi, call something to initialize
  -      OtherState%InitAcc = .true. 
  -   end if
      
      
      IF(p%analysis_type == 2) THEN
  
positive.code:          return
        end if
  
     call BD_Input_extrapinterp( u, utimes, u_interp, t+p%dt, ErrStat2, ErrMsg2 )
        call SetErrStat(ErrStat2,ErrMsg2,ErrStat,ErrMsg,RoutineName)
  !WRITE(*,*) 'u_interp'
  
negative.code:    PUBLIC :: BD_Tilde
     PUBLIC :: BD_MotionTensor
     PUBLIC :: BD_CalcIC
     PUBLIC :: BD_InitAcc
  
  CONTAINS
  
  