Re: [Quantlib-users] The reason of differences between `FDDividendAmericanEngine` of QuantLib 1.12 and `FdBlackScholesVanillaEngine` of QuantLib 1.18

[Shenze W. <she...@da...>]

Hi Klaus,

I understand that different dividend models have different assumptions about the underlying process of the stock price. So, the pricing results will be different.

But could you please help me check the pricing results in the following screenshot? It is an American call option with extremely low volatility and a dividend right before the expiry date. S = 100 and K =90. I think the value of this option should be very close to 10, which matches the result of the Spot dividend model. However, the pricing result from Escrowed dividend model is 0, which looks a little wired.

Thanks a lot for your patience.



Best,
Shenze


On Jun 26, 2020, 1:32 PM -0400, Klaus Spanderen <kl...@sp...>, wrote:
> Hi
> Spot dividend and escrowed dividend model are different models and are supposed to give different results for the same parameter set. An implied volatility calculated with the escrowed dividend model will not give the same price back when used in a spot dividend model because the underlying stochastic differential equations are different.
> best regards
> Klaus
> On Freitag, 26. Juni 2020 17:34:57 CEST Shenze Wang wrote:
> Hi Klaus,
>
> Thanks a lot for you explanations.
>
> I made more calculations. It seems that the differences between Spot dividend model and Escrowed dividend model are not only for pathologic cases. And also a greater number of time steps and grid points do not help. The calculation results are attached. So I guess that there may be something goes wrong with Spot dividend model.
>
> The difference between the two dividend model also causes another bug in impliedVolatility. Because for American options, FdBlackScholesVanillaEngine with Spot dividend model is always being used, when calculating ivol. Here is the issue I opened, https://github.com/lballabio/QuantLib/issues/850.
>
> I think maybe it is necessary to take a closer look at the two dividend models.
>
>
> Best,
> Shenze
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