---
title: math.jn() function
description: math.jn() returns the order-n Bessel function of the first kind.
url: https://docs.influxdata.com/flux/v0/stdlib/math/jn/
estimated_tokens: 917
product: Flux
version: v0
publisher: InfluxData
canonical: https://docs.influxdata.com/flux/v0/stdlib/math/jn/
date: '2024-04-08T16:01:02-06:00'
lastmod: '2024-04-08T16:01:02-06:00'
---

* Flux 0.22.0+

InfluxDB support

`math.jn()` returns the order-n Bessel function of the first kind.

##### Function type signature

```js
(n: int, x: float) => float
```

For more information, see [Function type signatures](/flux/v0/function-type-signatures/).

## Parameters

### n

(Required)
Order number.

### x

(Required)
Value to operate on.

## Examples

* [Return the order-n Bessel function of a value](#return-the-order-n-bessel-function-of-a-value)
* [Use math.jn in map](#use-mathjn-in-map)

### Return the order-n Bessel function of a value

```
import "math"

math.jn(n: 2, x: 1.23)// 0.16636938378681407

```

### Use math.jn in map

```js
import "sampledata"
import "math"

sampledata.float()
    |> map(fn: (r) => ({r with _value: math.jn(n: 4, x: r._value)}))
```

[](#view-example-input-and-output)

View example input and output

#### Input data

|       \_time       |\*tag|\_value|
|--------------------|-----|-------|
|2021-01-01T00:00:00Z| t1  |\-2.18 |
|2021-01-01T00:00:10Z| t1  | 10.92 |
|2021-01-01T00:00:20Z| t1  | 7.35  |
|2021-01-01T00:00:30Z| t1  | 17.53 |
|2021-01-01T00:00:40Z| t1  | 15.23 |
|2021-01-01T00:00:50Z| t1  | 4.43  |

|       \_time       |\*tag|\_value|
|--------------------|-----|-------|
|2021-01-01T00:00:00Z| t2  | 19.85 |
|2021-01-01T00:00:10Z| t2  | 4.97  |
|2021-01-01T00:00:20Z| t2  |\-3.75 |
|2021-01-01T00:00:30Z| t2  | 19.77 |
|2021-01-01T00:00:40Z| t2  | 13.86 |
|2021-01-01T00:00:50Z| t2  | 1.86  |

#### Output data

|       \_time       |       \_value        |\*tag|
|--------------------|----------------------|-----|
|2021-01-01T00:00:00Z| 0.046148335742456664 | t1  |
|2021-01-01T00:00:10Z|\-0.03367382202216673 | t1  |
|2021-01-01T00:00:20Z| 0.06455053599079605  | t1  |
|2021-01-01T00:00:30Z|\-0.016152633110842446| t1  |
|2021-01-01T00:00:40Z|\-0.15300380439231542 | t1  |
|2021-01-01T00:00:50Z|  0.3401384178914538  | t1  |

|       \_time       |      \_value       |\*tag|
|--------------------|--------------------|-----|
|2021-01-01T00:00:00Z|0.14801732445932958 | t2  |
|2021-01-01T00:00:10Z| 0.3896093468299793 | t2  |
|2021-01-01T00:00:20Z|0.24301709268606153 | t2  |
|2021-01-01T00:00:30Z|0.15603599253486927 | t2  |
|2021-01-01T00:00:40Z|0.10341672446511223 | t2  |
|2021-01-01T00:00:50Z|0.026150267042506597| t2  |
| _time | *tag | _value |
| --- | --- | --- |
| _time | *tag | _value |
| 2021-01-01T00:00:00Z | t1 | -2.18 |
| 2021-01-01T00:00:10Z | t1 | 10.92 |
| 2021-01-01T00:00:20Z | t1 | 7.35 |
| 2021-01-01T00:00:30Z | t1 | 17.53 |
| 2021-01-01T00:00:40Z | t1 | 15.23 |
| 2021-01-01T00:00:50Z | t1 | 4.43 |

| _time | *tag | _value |
| --- | --- | --- |
| _time | *tag | _value |
| 2021-01-01T00:00:00Z | t2 | 19.85 |
| 2021-01-01T00:00:10Z | t2 | 4.97 |
| 2021-01-01T00:00:20Z | t2 | -3.75 |
| 2021-01-01T00:00:30Z | t2 | 19.77 |
| 2021-01-01T00:00:40Z | t2 | 13.86 |
| 2021-01-01T00:00:50Z | t2 | 1.86 |

| _time | _value | *tag |
| --- | --- | --- |
| _time | _value | *tag |
| 2021-01-01T00:00:00Z | 0.046148335742456664 | t1 |
| 2021-01-01T00:00:10Z | -0.03367382202216673 | t1 |
| 2021-01-01T00:00:20Z | 0.06455053599079605 | t1 |
| 2021-01-01T00:00:30Z | -0.016152633110842446 | t1 |
| 2021-01-01T00:00:40Z | -0.15300380439231542 | t1 |
| 2021-01-01T00:00:50Z | 0.3401384178914538 | t1 |

| _time | _value | *tag |
| --- | --- | --- |
| _time | _value | *tag |
| 2021-01-01T00:00:00Z | 0.14801732445932958 | t2 |
| 2021-01-01T00:00:10Z | 0.3896093468299793 | t2 |
| 2021-01-01T00:00:20Z | 0.24301709268606153 | t2 |
| 2021-01-01T00:00:30Z | 0.15603599253486927 | t2 |
| 2021-01-01T00:00:40Z | 0.10341672446511223 | t2 |
| 2021-01-01T00:00:50Z | 0.026150267042506597 | t2 |