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

[Klaus S. <kl...@sp...>]

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[1].


I think maybe it is necessary to take a closer look at the two dividend models.




Best,
Shenze


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[1] https://github.com/lballabio/QuantLib/issues/850