anchor.diff:  
     use bl_constants_module, only: ZERO, THIRD, HALF, ONE, TWO
     use prob_params_module, only: center, problo
  -  use meth_params_module, only: do_rotation, rot_period
  +  use meth_params_module, only: do_rotation, rot_period, rot_period_dot
     use rot_sources_module, only: get_omega, cross_product
     
     implicit none
  
positive.code:   ! at large distances. There is some clipping due to material
    ! that leaves or enters the domain boundaries, but this should
    ! average out over time, and will be negligible in magnitude.
          
    theta = omega * time
  
    ! This is the 3D rotation matrix for converting between reference frames.
    ! It is the composition of rotations along the x, y, and z axes. Therefore 
    ! it allows for the case where we are rotating about multiple axes. Normally 
  
negative.code: 
    dV = dx(1) * dx(2) * dx(3)
    dQtt(:,:) = ZERO
    
    ! If we are in a rotating reference frame, then we want
    ! to rotate this by an amount corresponding to the time
    ! that has passed since the beginning of the simulation.
  