def rect_to_cyl_vec(vx,vy,vz,X,Y,Z,cyl=False):
    """
    NAME:

       rect_to_cyl_vec

    PURPOSE:

       transform vectors from rectangular to cylindrical coordinates vectors

    INPUT:

       vx - 

       vy - 

       vz - 

       X - X

       Y - Y

       Z - Z

       cyl - if True, X,Y,Z are already cylindrical

    OUTPUT:

       vR,vT,vz

    HISTORY:

       2010-09-24 - Written - Bovy (NYU)

    """
    if not cyl:
        R,phi,Z= rect_to_cyl(X,Y,Z)
    else:
        phi= Y
    vr=+vx*sc.cos(phi)+vy*sc.sin(phi)
    vt= -vx*sc.sin(phi)+vy*sc.cos(phi)
    return (vr,vt,vz)
NAME:

       rect_to_cyl_vec

    PURPOSE:

       transform vectors from rectangular to cylindrical coordinates vectors

    INPUT:

       vx - 

       vy - 

       vz - 

       X - X

       Y - Y

       Z - Z

       cyl - if True, X,Y,Z are already cylindrical

    OUTPUT:

       vR,vT,vz

    HISTORY:

       2010-09-24 - Written - Bovy (NYU)