def interpol_expon(x, x0, y0, x1, y1, exp):
    """
    interpolate between (x0, y0) and (x1, y1) at point x

    exp defines the exponential of the curve
    """
    dx = (x - x0) / (x1 - x0)
    return y0 + pow(dx, exp) * (y1 - y0)
