---
title: math.j0() function
description: math.j0() returns the order-zero Bessel function of the first kind.
url: https://docs.influxdata.com/flux/v0/stdlib/math/j0/
estimated_tokens: 1416
product: Flux
version: v0
---

# math.j0() function

-   Flux 0.22.0+
-   View InfluxDB support

`math.j0()` returns the order-zero Bessel function of the first 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.j0 in map](#use-mathj0-in-map)

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

```js
import "math"

math.j0(x: 1.23)// 0.656070571706025

```

### Use math.j0 in map

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

sampledata.float()
    |> map(fn: (r) => ({r with _value: math.j0(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 | 0.12150949471274336 | t1 |
| 2021-01-01T00:00:10Z | -0.1848208162077201 | t1 |
| 2021-01-01T00:00:20Z | 0.2837448367876356 | t1 |
| 2021-01-01T00:00:30Z | -0.09816636158288365 | t1 |
| 2021-01-01T00:00:40Z | -0.0602560278685108 | t1 |
| 2021-01-01T00:00:50Z | -0.3360414225378073 | t1 |

| _time | _value | *tag |
| --- | --- | --- |
| 2021-01-01T00:00:00Z | 0.17516950223786715 | t2 |
| 2021-01-01T00:00:10Z | -0.18737219444686604 | t2 |
| 2021-01-01T00:00:20Z | -0.4014060549361743 | t2 |
| 2021-01-01T00:00:30Z | 0.1779340476167977 | t2 |
| 2021-01-01T00:00:40Z | 0.18809934034815845 | t2 |
| 2021-01-01T00:00:50Z | 0.30507973268984145 | t2 |