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bug report: negative price for an American put option using Bjerksund and Stensland approximation

Posted by jan.willem.bikker on Nov 09, 2005; 12:31am
URL: http://quantlib.414.s1.nabble.com/bug-report-negative-price-for-an-American-put-option-using-Bjerksund-and-Stensland-approximation-tp4195.html


Hello,

I have a bug report: I encountered a  negative price for an American put option using Bjerksund and Stensland approximation.

I used the setting of the example from QuantLib-0.3.8\Examples\AmericanOption\AmericanOption.cpp  as a basis for my program.

The settings are

SettlementDate=38353
ExerciseDate=42003 = SettlementDate +10*365
strike=100
spot=125
vol=0.05
interest=0.1
dividend=0.05
option type = put

and

        option.setPricingEngine(boost::shared_ptr<PricingEngine>(
                new BjerksundStenslandApproximationEngine));
        aBjStprice = option.NPV();

yields

        aBjStprice =-25

Furthermore, changing the spot to 100 yields a price of 0, which also seems incorrect.

I've checked in total 85 american options in various scenarios, and these are the only two behaving strangely (the rest is comparable to the binomial CCR method).

I hope somebody finds this message useful. I couldn't find this bug on sourceforge.

Kind regards,

Jan Willem Bikker

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