http://quantlib.414.s1.nabble.com/Statistics-Value-at-risk-tp15687p15720.html
250 < 0.01, F(-0.04) = 3 / 250 >= 0.01, I think. So QuantLib seems to
> Thanks, Luigi. But, I have made the test, the result should be between 0.04,
> and 0.05, not exactly the 0.04. But, lower than 0.045. I donot know why.
>
> regards
>
> Alex
>
>
> 2014-08-07 22:51 GMT+08:00 Luigi Ballabio <
[hidden email]>:
>
>> The code below doesn't interpolate. In your case, if you ask for 0.99
>> VaR, the second loss is 0.05 and the third is 0.04, it just returns
>> 0.04.
>>
>> I don't think I remember the reason for that, though.
>>
>> Luigi
>>
>>
>> On Thu, Aug 7, 2014 at 1:19 PM, Yuanhao Zhang <
[hidden email]>
>> wrote:
>> > Forgot to attach the excel file there.
>> > Hi, I am totally confused by the quantlib percentile function, the code
>> > is
>> > listed below. I have attached an excel file, you can find the issue in
>> > sheet1. If I have 250 sample pnl, the 0.99 percentile is just between
>> > the
>> > second and third one, use the interpolated function the value I have
>> > highlighted there. But, the result of QL is smaller than the highlighted
>> > one. And I thought the result of Excel is right, I have read the code,
>> > but i
>> > can not understand it, could you explain it for me. thanks!
>> >
>> > Real GeneralStatistics::percentile(Real percent) const {
>> >
>> > QL_REQUIRE(percent > 0.0 && percent <= 1.0,
>> > "percentile (" << percent << ") must be in (0.0,
>> > 1.0]");
>> >
>> > Real sampleWeight = weightSum();
>> > QL_REQUIRE(sampleWeight>0.0,
>> > "empty sample set");
>> >
>> > sort();
>> >
>> > std::vector<std::pair<Real,Real> >::iterator k, l;
>> > k = samples_.begin();
>> > l = samples_.end()-1;
>> > /* the sum of weight is non null, therefore there's
>> > at least one sample */
>> > Real integral = k->second, target = percent*sampleWeight;
>> > while (integral < target && k != l) {
>> > k++;
>> > integral += k->second;
>> > }
>> > return k->first;
>> > }
>> >
>> >
>> >
>> > 2014-08-07 18:10 GMT+08:00 Luigi Ballabio <
[hidden email]>:
>> >>
>> >> What are you getting instead? May you post some sample code that
>> >>
>> >> reproduces the issue?
>> >>
>> >> Luigi
>> >>
>> >> On Wed, Aug 6, 2014 at 6:20 PM, Yuanhao Zhang <
[hidden email]>
>> >> wrote:
>> >> > Does any one used Statistics Value at risk function in QuantLib? I
>> >> > try
>> >> > to
>> >> > use the simple 250 PnL sample to test this function. The confidence
>> >> > level is
>> >> > 0.99, so the value should be between the second one and the third
>> >> > one.
>> >> > If
>> >> > the second one is -0.04 and the third one is -0.05, so the value is
>> >> > -(-0.04+(-0.05))/2=0.045. But, the quantlib value is always smaller
>> >> > than
>> >> > 0.045. Is that wrong with the calculation logic? I can not figure it
>> >> > out
>> >> > why
>> >> > the value is different. Any one could help me figure it out?
>> >> >
>> >> > Best regards
>> >> >
>> >> > Alex
>> >> >
>> >> >
>> >> >
>> >> > ------------------------------------------------------------------------------
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>> >> >
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>> >>
>> >>
>> >>
>> >> --
>> >> <
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>> >> <
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>> >
>> >
>>
>>
>>
>> --
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>> <
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>
>
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