---
title: math.jn() function
description: >
  `math.jn()` returns the order-n Bessel function of the first kind.
menu:
  flux_v0_ref:
    name: math.jn
    parent: math
    identifier: math/jn
weight: 101
---

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



##### Function type signature

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

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

## Parameters

### n
({{< req >}})
Order number.



### x
({{< req >}})
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

```js
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)}))

```

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{{% expand "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   |

{{% /expand %}}
{{< /expand-wrapper >}}