# Decay Function question **URL:** \ **Category:** Elasticsearch\ **Created:** [November 6, 2014, 7:07pm UTC](https://discuss.elastic.co/t/decay-function-question/20615 "2014-11-06T19:07:39Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![marlo](https://avatars.discourse-cdn.com/v4/letter/m/d26b3c/32.png) [@marlo](https://discuss.elastic.co/u/marlo)\ **Post date:** [November 6, 2014, 7:07pm UTC](https://discuss.elastic.co/t/decay-function-question/20615/1 "2014-11-06T19:07:39Z")
I've begun using the decay function in order to promote more recent results in our index. In particular I'm using what's documented here: [http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/query-dsl-function-score-query.html](http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/query-dsl-function-score-query.html) Here's the date example they use (let's assume gaussian slope): ``` "DECAY_FUNCTION": { "FIELD_NAME": { "origin": "2013-09-17", "scale": "10d", "offset": "5d", "decay" : 0.5 } } ``` So in trying to visualize this decay, is it safe to make the following assumptions in terms of associating these input values to a graph: - origin is the start (x-value) of the slope, in this case the date 9/17/2013 - for all points up to offset, the slope is flat, so there's no negative scoring for the 5 days after 9/17/2013 - the "end" of the slope is scale - at the data point 'scale', the slope will have a y-value (on the graph) of decay (0.5) The last point I am not so sure about. Furthermore, I'm unclear as to what happens for articles outside of scale, so past 10 days. My test show that they actually get a 'zero' multiplier for their score, so basically their scores all end up being zero. I was under the impression that they would get a score multiplier of 0.5. Any help would be appreciated. -- You received this message because you are subscribed to the Google Groups "elasticsearch" group. To unsubscribe from this group and stop receiving emails from it, send an email to [elasticsearch+unsubscribe@googlegroups.com](mailto:elasticsearch+unsubscribe@googlegroups.com). To view this discussion on the web visit [https://groups.google.com/d/msgid/elasticsearch/32d518ad-2b63-4f13-a952-0f408722bd79%40googlegroups.com](https://groups.google.com/d/msgid/elasticsearch/32d518ad-2b63-4f13-a952-0f408722bd79%40googlegroups.com). For more options, visit [https://groups.google.com/d/optout](https://groups.google.com/d/optout). ---
**Author:** ![Britta\_Weber](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/britta_weber/32/1113_2.png) [@Britta\_Weber](https://discuss.elastic.co/u/Britta_Weber)\ **Post date:** [November 10, 2014, 10:06am UTC](https://discuss.elastic.co/t/decay-function-question/20615/2 "2014-11-10T10:06:42Z")
Hi Mario, I added an image which hopefully explains a little better how decay functions work here: > > - origin is the start (x-value) of the slope, in this case the date 9/17/2013 yes > - for all points up to offset, the slope is flat, so there's no negative scoring for the 5 days after 9/17/2013 The decay function never returns a negative value. It will always be between 0 and 1. For each value within +- offset from the defined origin the decay function will just return 1. > - the "end" of the slope is scale No, decay function will decrease further. The scale parameter just steers how quickly the function approaches 0. - at the data point 'scale', the slope will have a y-value (on the graph) of decay (0.5) yes. > My test show that they actually get a 'zero' multiplier for their score, so basically their scores all end up being zero. I was under the impression that they would get a score multiplier of 0.5. No, the score will decrease further until it reaches 0. If you need to have documents outside the "scale" range to have a value of 0.5 you need to define a separate function which then adjusts the score for these documents as needed. On Thu, Nov 6, 2014 at 8:07 PM, Marlo Epres [mepres@gmail.com](mailto:mepres@gmail.com) wrote: > I've begun using the decay function in order to promote more recent results > in our index. In particular I'm using what's documented here: > > [Elasticsearch Platform — Find real-time answers at scale | Elastic](http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/query-dsl-function-score-query.html) > > Here's the date example they use (let's assume gaussian slope): > > ``` > "DECAY_FUNCTION": { > "FIELD_NAME": { > "origin": "2013-09-17", > "scale": "10d", > "offset": "5d", > "decay" : 0.5 > } > } > > ``` > > So in trying to visualize this decay, is it safe to make the following > assumptions in terms of associating these input values to a graph: > > - origin is the start (x-value) of the slope, in this case the date > 9/17/2013 > - for all points up to offset, the slope is flat, so there's no negative > scoring for the 5 days after 9/17/2013 > - the "end" of the slope is scale > - at the data point 'scale', the slope will have a y-value (on the graph) of > decay (0.5) > > The last point I am not so sure about. Furthermore, I'm unclear as to what > happens for articles outside of scale, so past 10 days. My test show that > they actually get a 'zero' multiplier for their score, so basically their > scores all end up being zero. I was under the impression that they would get > a score multiplier of 0.5. Any help would be appreciated. > > -- > You received this message because you are subscribed to the Google Groups > "elasticsearch" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [elasticsearch+unsubscribe@googlegroups.com](mailto:elasticsearch+unsubscribe@googlegroups.com). > To view this discussion on the web visit > [https://groups.google.com/d/msgid/elasticsearch/32d518ad-2b63-4f13-a952-0f408722bd79%40googlegroups.com](https://groups.google.com/d/msgid/elasticsearch/32d518ad-2b63-4f13-a952-0f408722bd79%40googlegroups.com). > For more options, visit [https://groups.google.com/d/optout](https://groups.google.com/d/optout). -- You received this message because you are subscribed to the Google Groups "elasticsearch" group. To unsubscribe from this group and stop receiving emails from it, send an email to [elasticsearch+unsubscribe@googlegroups.com](mailto:elasticsearch+unsubscribe@googlegroups.com). To view this discussion on the web visit [https://groups.google.com/d/msgid/elasticsearch/CALhJbBimcB2xX49FqyXyXye7ZUrsq3gDPT31gHF0p4%2B3q%2BaXRA%40mail.gmail.com](https://groups.google.com/d/msgid/elasticsearch/CALhJbBimcB2xX49FqyXyXye7ZUrsq3gDPT31gHF0p4%2B3q%2BaXRA%40mail.gmail.com). For more options, visit [https://groups.google.com/d/optout](https://groups.google.com/d/optout). ---
**Author:** ![system](https://us1.discourse-cdn.com/elastic/original/3X/1/a/1ac57faf039f6b580b3f104ef42a2a89e41014de.png) [@system](https://discuss.elastic.co/u/system)\ **Post date:** [July 6, 2017, 12:51am UTC](https://discuss.elastic.co/t/decay-function-question/20615/3 "2017-07-06T00:51:10Z")