到期收益率

def solve(face_value, coupon_rate, market_price, maturity):
    coupon = face_value * coupon_rate
    ytm_low, ytm_high = 0.01, 0.5
    for _ in range(100):
        ytm = (ytm_low + ytm_high) / 2
        price = sum(coupon / (1 + ytm) ** t for t in range(1, maturity + 1))
        price += face_value / (1 + ytm) ** maturity
        if abs(price - market_price) < 0.01:
            break
        if price > market_price:
            ytm_low = ytm
        else:
            ytm_high = ytm
    return {"面值": face_value, "市场价格": market_price, "YTM": round(ytm, 4)}