# Need definition of log1p,log2p, ln1p, and ln2p of field\_value\_factor modifier

**URL:** <https://discuss.elastic.co/t/need-definition-of-log1p-log2p-ln1p-and-ln2p-of-field-value-factor-modifier/29101>\
**Category:** Elasticsearch\
**Created:** [September 11, 2015, 8:14am UTC](https://discuss.elastic.co/t/need-definition-of-log1p-log2p-ln1p-and-ln2p-of-field-value-factor-modifier/29101 "2015-09-11T08:14:30Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![ivern](https://avatars.discourse-cdn.com/v4/letter/i/c6cbf5/32.png) [@ivern](https://discuss.elastic.co/u/ivern)\
**Post date:** [September 11, 2015, 8:14am UTC](https://discuss.elastic.co/t/need-definition-of-log1p-log2p-ln1p-and-ln2p-of-field-value-factor-modifier/29101/1 "2015-09-11T08:14:30Z")

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Hi All,

I found that field\_value\_factor modifier could be none, log, log1p, log2p, ln, ln1p,ln2p, square, sqrt, or reciprocal.  
I am not sure about the definition of these modifiers:

1. log1p = log(1+p)
2. log2p = log(2p) -\> from wolfram alpha
3. ln1p = ln(1+p)
4. ln2p = ln(2p)

In wolfram alpha, defintion of #1 is ln(1+x).

CMIIW

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**Author:** ![colings86](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/colings86/32/44960_2.png) [@colings86](https://discuss.elastic.co/u/colings86)\
**Post date:** [September 11, 2015, 11:06am UTC](https://discuss.elastic.co/t/need-definition-of-log1p-log2p-ln1p-and-ln2p-of-field-value-factor-modifier/29101/2 "2015-09-11T11:06:51Z")

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I have raised [https://github.com/elastic/elasticsearch/issues/13511](https://github.com/elastic/elasticsearch/issues/13511) to update the documentation but in the mean time, from looking at the code in FieldValueFactorFunction.Modifier:

for a value n:

1. log1p = Math.log10(n + 1)
2. log2p = Math.log10(n + 2)
3. ln1p = Math.log1p(n) = Math.log(n + 1) [= ln(n + 1)]
4. ln2p = Math.log2p(n + 1) = Math.log(n + 2) [= ln(n + 2)]

Hope that helps

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**Author:** ![ivern](https://avatars.discourse-cdn.com/v4/letter/i/c6cbf5/32.png) [@ivern](https://discuss.elastic.co/u/ivern)\
**Post date:** [September 11, 2015, 1:07pm UTC](https://discuss.elastic.co/t/need-definition-of-log1p-log2p-ln1p-and-ln2p-of-field-value-factor-modifier/29101/3 "2015-09-11T13:07:32Z")

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Thanks, it really helps

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**Author:** ![system](https://us1.discourse-cdn.com/elastic/original/3X/1/a/1ac57faf039f6b580b3f104ef42a2a89e41014de.png) [@system](https://discuss.elastic.co/u/system)\
**Post date:** [July 5, 2017, 11:50pm UTC](https://discuss.elastic.co/t/need-definition-of-log1p-log2p-ln1p-and-ln2p-of-field-value-factor-modifier/29101/4 "2017-07-05T23:50:44Z")

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