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From Sean Owen <sro...@gmail.com>
Subject Re: What equation do NDCG used ?
Date Wed, 04 Apr 2012 21:23:57 GMT
It does use the order:

double discount = i == 0 ? 1.0 : 1.0 / log2(i + 1);

The "score" you gain for recommending a relevant item decreases as you
go down the list of recommendations.

As the comments in the code note, relevance is 1 for relevant items
and 0 for others. There is no point in showing a term multiplied by 1,
or 0.

On Wed, Apr 4, 2012 at 10:19 PM, ziad kamel <ziad.kamel25@gmail.com> wrote:
> DCG should check the order and the formula seems not , just check if
> it contains the item
>
>  if (relevantItemIDs.contains(item.getItemID())) {
>          cumulativeGain += discount;
>        }
>
> Second thing is that it have a relevance number "rel" which the
> formula don't use.
>
>
>
>
> On Wed, Apr 4, 2012 at 3:54 PM, Sean Owen <srowen@gmail.com> wrote:
>> It's the same formula, what do you think is different?
>>
>> On Wed, Apr 4, 2012 at 9:35 PM, ziad kamel <ziad.kamel25@gmail.com> wrote:
>>> Hi , I checked the code for NDCG and it seems not same as
>>> http://en.wikipedia.org/wiki/Discounted_cumulative_gain
>>> How that formula was derived ?
>>>
>>> Thanks

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