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Recommend use of ln1p/log1p to avoid negative scores (#41610) 

As negative scores will now cause an error, and it is easy to
accidentally produce negative scores with some of the built-in modifiers
(especially `ln` and `log`), this adjusts the documentation to more
strongly recommend the use of `ln1p` and `log1p` instead.

Also corrects some awkward formatting on the note sections following the
table.
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Gordon Brown 2019-05-03 09:10:29 -06:00 committed by GitHub
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23
docs/reference/query-dsl/function-score-query.asciidoc
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@ -305,10 +305,14 @@ There are a number of options for the `field_value_factor` function:
| Modifier | Meaning
| `none` | Do not apply any multiplier to the field value
| `log` | Take the https://en.wikipedia.org/wiki/Common_logarithm[common logarithm] of the field value
| `log` | Take the https://en.wikipedia.org/wiki/Common_logarithm[common logarithm] of the field value.
Because this function will return a negative value and cause an error if used on values
between 0 and 1, it is recommended to use `log1p` instead.
| `log1p` | Add 1 to the field value and take the common logarithm
| `log2p` | Add 2 to the field value and take the common logarithm
| `ln` | Take the https://en.wikipedia.org/wiki/Natural_logarithm[natural logarithm] of the field value
| `ln` | Take the https://en.wikipedia.org/wiki/Natural_logarithm[natural logarithm] of the field value.
Because this function will return a negative value and cause an error if used on values
between 0 and 1, it is recommended to use `ln1p` instead.
| `ln1p` | Add 1 to the field value and take the natural logarithm
| `ln2p` | Add 2 to the field value and take the natural logarithm
| `square` | Square the field value (multiply it by itself)
@ -321,14 +325,17 @@ There are a number of options for the `field_value_factor` function:
Value used if the document doesn't have that field. The modifier
and factor are still applied to it as though it were read from the document.
NOTE: Scores produced by the `field_value_score` function must be
non-negative, otherwise an error will be thrown. The `log` and `ln` modifiers
will produce negative values if used on values between 0 and 1. Be sure to limit
the values of the field with a range filter to avoid this, or use `log1p` and
`ln1p`.
Keep in mind that taking the log() of 0, or the square root of a negative number
is an illegal operation, and an exception will be thrown. Be sure to limit the
values of the field with a range filter to avoid this, or use `log1p` and
`ln1p`.
NOTE: Keep in mind that taking the log() of 0, or the square root of a
negative number is an illegal operation, and an exception will be thrown. Be
sure to limit the values of the field with a range filter to avoid this, or use
`log1p` and `ln1p`.
NOTE: Scores produced by the `field_value_score` function must be non-negative,
otherwise an error will be thrown.
[[function-decay]]
==== Decay functions