def setbox(x, y, mbox, xmax, ymax):
    """Create a box of length mbox around a position x,y.   If the box will
       be out of [0,len] then reset the edges of the box to be within the
       boundaries

       Parameters
       ----------
       x : int
           Central x-position of box

       y : int
           Central y-position of box

       mbox : int
           Width of box

       xmax : int
           Maximum x value

       ymax : int
           Maximum y value

        Returns
        -------
        x1 :  int
           Lower x corner of box

        x2 :  int
           Upper x corner of box

        y1 :  int
           Lower y corner of box

        y2 :  int
           Upper y corner of box
    """
    mbox = max(int(0.5 * mbox), 1)
    y1 = max(0, y - mbox)
    y2 = min(y + mbox + 1, ymax - 1)
    x1 = max(0, x - mbox)
    x2 = min(x + mbox + 1, xmax - 1)

    return x1, x2, y1, y2