SUBROUTINE transform(theta,px_in, p_total, px, py)
     
  USE nrtype
  USE precision_def
  USE parameters ! module with coordinates and constants
  IMPLICIT NONE
  REAL(RP), INTENT(IN) :: theta
  REAL(RP), INTENT(INOUT) :: px_in, p_total, px,py

    
  !Change into cartesian coordinates

  px = px_in*sin(theta) + p_total*cos(theta)
  py = px_in*cos(theta) - p_total*sin(theta)



END SUBROUTINE transform