def cheb1ord(wp, ws, gpass, gstop, analog=False):
    wp = atleast_1d(wp)
    ws = atleast_1d(ws)
    filter_type = 2 * (len(wp) - 1)
    if wp[0] < ws[0]:
        filter_type += 1
    else:
        filter_type += 2

    # Pre-warp frequencies for digital filter design
    if not analog:
        passb = tan(pi * wp / 2.0)
        stopb = tan(pi * ws / 2.0)
    else:
        passb = wp * 1.0
        stopb = ws * 1.0

    if filter_type == 1:           # low
        nat = stopb / passb
    elif filter_type == 2:          # high
        nat = passb / stopb
    elif filter_type == 3:     # stop
        wp0 = optimize.fminbound(band_stop_obj, passb[0], stopb[0] - 1e-12,
                                 args=(0, passb, stopb, gpass, gstop, 'cheby'),
                                 disp=0)
        passb[0] = wp0
        wp1 = optimize.fminbound(band_stop_obj, stopb[1] + 1e-12, passb[1],
                                 args=(1, passb, stopb, gpass, gstop, 'cheby'),
                                 disp=0)
        passb[1] = wp1
        nat = ((stopb * (passb[0] - passb[1])) /
               (stopb ** 2 - passb[0] * passb[1]))
    elif filter_type == 4:  # pass
        nat = ((stopb ** 2 - passb[0] * passb[1]) /
               (stopb * (passb[0] - passb[1])))

    nat = min(abs(nat))

    GSTOP = 10 ** (0.1 * abs(gstop))
    GPASS = 10 ** (0.1 * abs(gpass))
    ord = int(ceil(arccosh(sqrt((GSTOP - 1.0) / (GPASS - 1.0))) /
                   arccosh(nat)))

    # Natural frequencies are just the passband edges
    if not analog:
        wn = (2.0 / pi) * arctan(passb)
    else:
        wn = passb

    if len(wn) == 1:
        wn = wn[0]
    return ord, wn
Chebyshev type I filter order selection.
dataset/ETHPy150Open scipy/scipy/scipy/signal/filter_design.py/cheb1ord