def kernel_primitive_zhao(x, s0=0.08333, theta=0.242):
    """
    Calculates the primitive of the Zhao kernel for given values.

    :param x: point to evaluate
    :param s0: initial reaction time
    :param theta: empirically determined constant
    :return: primitive evaluated at x
    """
    c0 = 1.0 / s0 / (1 - 1.0 / -theta)
    if x < 0:
        return 0
    elif x <= s0:
        return c0 * x
    else:
        return c0 * (s0 + (s0 * (1 - (x / s0)**-theta)) / theta)