---
title: math.y0() function
description: >
  `math.y0()` returns the order-zero Bessel function of the second kind.
menu:
  flux_v0_ref:
    name: math.y0
    parent: math
    identifier: math/y0
weight: 101
---

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



##### Function type signature

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

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

## Parameters

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

```

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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 | 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   |

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