def sheet_to_cyl(x,y,vx,vy,t,sheet):
    """Convert from shearing-sheet coordinates to cylindrical coordinates

Parameters
----------
x: float or array
    x coordinate in the sheet
y: float or array
    y coordinate in the sheet
vx: float or array
    x velocity in the sheet
vy: float or array
    y velocity in the sheet
t: float or array
    Time
sheet: dict
    Dictionary that describes the sheet

Returns
-------
float or array
    (R,phi,vR,vT) cylindrical coordinates    
    """
    return (sheet['R0']+x,
            (y+sheet['R0']*sheet['Omega0']*t)/sheet['R0'],
            vx,
            (sheet['R0']+x)/sheet['R0']*(vy+sheet['R0']*sheet['Omega0']))