---
title: math.y0() function
description: math.y0() returns the order-zero Bessel function of the second kind.
url: https://docs.influxdata.com/flux/v0/stdlib/math/y0/
estimated_tokens: 1409
product: Flux
version: v0
---

# math.y0() function

-   Flux 0.22.0+
-   View InfluxDB support

`math.y0()` returns the order-zero Bessel function of the second kind.

##### Function type signature

```js
(x: float) => float
```

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

## Parameters

### x

(Required) Value to operate on.

## Examples

-   [Return the order-zero Bessel function of a value](#return-the-order-zero-bessel-function-of-a-value)
-   [Use math.y0 in map](#use-mathy0-in-map)

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

```js
import "math"

math.y0(x: 3.14)// 0.3289375969127807

```

### Use math.y0 in map

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

sampledata.float()
    |> map(fn: (r) => ({r with _value: math.y0(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 | NaN | t1 |
| 2021-01-01T00:00:10Z | -0.15517570189175475 | t1 |
| 2021-01-01T00:00:20Z | 0.07687091351245329 | t1 |
| 2021-01-01T00:00:30Z | -0.16329326302215585 | t1 |
| 2021-01-01T00:00:40Z | 0.19531314382470338 | t1 |
| 2021-01-01T00:00:50Z | -0.17300760424559283 | t1 |

| _time | _value | *tag |
| --- | --- | --- |
| 2021-01-01T00:00:00Z | 0.03710847827981653 | t2 |
| 2021-01-01T00:00:10Z | -0.3039299357361664 | t2 |
| 2021-01-01T00:00:20Z | NaN | t2 |
| 2021-01-01T00:00:30Z | 0.023033101962350977 | t2 |
| 2021-01-01T00:00:40Z | 0.10257274599514705 | t2 |
| 2021-01-01T00:00:50Z | 0.4897750655109666 | t2 |