128 lines
3.6 KiB
Markdown
128 lines
3.6 KiB
Markdown
---
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title: math.log1p() function
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description: >
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`math.log1p()` returns the natural logarithm of 1 plus `x`.
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This operation is more accurate than `math.log(x: 1 + x)` when `x` is
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near zero.
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menu:
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flux_v0_ref:
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name: math.log1p
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parent: math
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identifier: math/log1p
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weight: 101
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---
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<!------------------------------------------------------------------------------
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IMPORTANT: This page was generated from comments in the Flux source code. Any
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edits made directly to this page will be overwritten the next time the
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documentation is generated.
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To make updates to this documentation, update the function comments above the
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function definition in the Flux source code:
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https://github.com/influxdata/flux/blob/master/stdlib/math/math.flux#L1459-L1459
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Contributing to Flux: https://github.com/influxdata/flux#contributing
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Fluxdoc syntax: https://github.com/influxdata/flux/blob/master/docs/fluxdoc.md
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------------------------------------------------------------------------------->
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`math.log1p()` returns the natural logarithm of 1 plus `x`.
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This operation is more accurate than `math.log(x: 1 + x)` when `x` is
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near zero.
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##### Function type signature
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```js
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(x: float) => float
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```
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{{% caption %}}
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For more information, see [Function type signatures](/flux/v0/function-type-signatures/).
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{{% /caption %}}
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## Parameters
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### x
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({{< req >}})
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Value to operate on.
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## Examples
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- [Return the natural logarithm of values near zero](#return-the-natural-logarithm-of-values-near-zero)
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- [Use math.log1p in map](#use-mathlog1p-in-map)
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### Return the natural logarithm of values near zero
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```js
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import "math"
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math.log1p(x: 0.56)// 0.44468582126144574
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```
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### Use math.log1p in map
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```js
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import "math"
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data
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|> map(fn: (r) => ({r with _value: math.log1p(x: r._value)}))
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```
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{{< expand-wrapper >}}
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{{% expand "View example input and output" %}}
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#### Input data
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| _time | *tag | _value |
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| -------------------- | ---- | --------------------- |
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| 2021-01-01T00:00:00Z | t1 | -0.021800000000000003 |
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| 2021-01-01T00:00:10Z | t1 | 0.1092 |
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| 2021-01-01T00:00:20Z | t1 | 0.0735 |
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| 2021-01-01T00:00:30Z | t1 | 0.1753 |
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| 2021-01-01T00:00:40Z | t1 | 0.15230000000000002 |
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| 2021-01-01T00:00:50Z | t1 | 0.0443 |
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| _time | *tag | _value |
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| -------------------- | ---- | -------------------- |
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| 2021-01-01T00:00:00Z | t2 | 0.1985 |
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| 2021-01-01T00:00:10Z | t2 | 0.0497 |
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| 2021-01-01T00:00:20Z | t2 | -0.0375 |
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| 2021-01-01T00:00:30Z | t2 | 0.1977 |
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| 2021-01-01T00:00:40Z | t2 | 0.1386 |
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| 2021-01-01T00:00:50Z | t2 | 0.018600000000000002 |
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#### Output data
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| _time | _value | *tag |
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| -------------------- | -------------------- | ---- |
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| 2021-01-01T00:00:00Z | -0.02204113087688024 | t1 |
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| 2021-01-01T00:00:10Z | 0.10363903475948592 | t1 |
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| 2021-01-01T00:00:20Z | 0.07092433833669866 | t1 |
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| 2021-01-01T00:00:30Z | 0.1615234341566714 | t1 |
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| 2021-01-01T00:00:40Z | 0.14175994503783176 | t1 |
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| 2021-01-01T00:00:50Z | 0.04334680450336586 | t1 |
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| _time | _value | *tag |
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| -------------------- | -------------------- | ---- |
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| 2021-01-01T00:00:00Z | 0.181070774892302 | t2 |
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| 2021-01-01T00:00:10Z | 0.048504409059614985 | t2 |
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| 2021-01-01T00:00:20Z | -0.03822121282019776 | t2 |
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| 2021-01-01T00:00:30Z | 0.18040305097132403 | t2 |
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| 2021-01-01T00:00:40Z | 0.12979943753484446 | t2 |
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| 2021-01-01T00:00:50Z | 0.018429135468367195 | t2 |
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{{% /expand %}}
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{{< /expand-wrapper >}}
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