code: def cyl_to_rect_vec(vr,vt,vz,phi):
      
      vx= vr*sc.cos(phi)-vt*sc.sin(phi)
      vy= vr*sc.sin(phi)+vt*sc.cos(phi)
      return (vx,vy,vz)
docs: NAME:
  
         cyl_to_rect_vec
  
      PURPOSE:
  
         transform vectors from cylindrical to rectangular coordinate vectors
  
      INPUT:
  
         vr - radial velocity
  
         vt - tangential velocity
  
         vz - vertical velocity
  
         phi - azimuth
  
      OUTPUT:
  
         vx,vy,vz
  
      HISTORY:
  
         2011-02-24 - Written - Bovy (NYU)