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

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`math.yn()` returns the order-n Bessel function of the second kind.



##### Function type signature

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

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

### n
({{< req >}})
Order number to use in the operation.



### 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.yn in map](#use-mathyn-in-map)

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

```js
import "math"

math.yn(n: 3, x: 3.14)// -0.4866506930335083


```


### Use math.yn in map

```js
import "math"

data
    |> map(fn: (r) => ({_time: r._time, _value: math.yn(n: r.n, x: r.x)}))

```

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#### Input data

| _time                | x   | n  |
| -------------------- | --- | -- |
| 2021-01-01T00:00:00Z | 1.2 | 3  |
| 2021-01-01T01:00:00Z | 2.4 | 4  |
| 2021-01-01T02:00:00Z | 3.6 | 5  |
| 2021-01-01T03:00:00Z | 4.8 | 6  |
| 2021-01-01T04:00:00Z | 5.1 | 7  |


#### Output data

| _time                | _value              |
| -------------------- | ------------------- |
| 2021-01-01T00:00:00Z | -3.589899629613186  |
| 2021-01-01T01:00:00Z | -1.6023565737844263 |
| 2021-01-01T02:00:00Z | -1.0581497196727103 |
| 2021-01-01T03:00:00Z | -0.8050704522628885 |
| 2021-01-01T04:00:00Z | -1.1643613692219157 |

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