code: def vxvyvz_to_galcencyl(vx,vy,vz,X,Y,Z,vsun=[0.,1.,0.],Xsun=1.,Zsun=0.,
                          galcen=False,_extra_rot=True):
      
      vxyz= vxvyvz_to_galcenrect(vx,vy,vz,vsun=vsun,Xsun=Xsun,Zsun=Zsun,
                                 _extra_rot=_extra_rot)
      return nu.array(\
          rect_to_cyl_vec(vxyz[:,0],vxyz[:,1],vxyz[:,2],X,Y,Z,cyl=galcen)).T
docs: NAME:
  
         vxvyvz_to_galcencyl
  
      PURPOSE:
  
         transform velocities in XYZ coordinates (wrt Sun) to cylindrical Galactocentric coordinates for velocities
  
      INPUT:
  
         vx - U
  
         vy - V
  
         vz - W
  
         X - X in Galactocentric rectangular coordinates
  
         Y - Y in Galactocentric rectangular coordinates
  
         Z - Z in Galactocentric rectangular coordinates
  
         vsun - velocity of the sun in the GC frame ndarray[3]
  
         Xsun - cylindrical distance to the GC
         
         Zsun - Sun's height above the midplane
  
         galcen - if True, then X,Y,Z are in cylindrical Galactocentric coordinates rather than rectangular coordinates
  
         _extra_rot= (True) if True, perform an extra tiny rotation to align the Galactocentric coordinate frame with astropy's definition
  
      OUTPUT:
  
         vRg, vTg, vZg
  
      HISTORY:
  
         2010-09-24 - Written - Bovy (NYU)