---
title: math.j0() function
description: >
  `math.j0()` returns the order-zero Bessel function of the first kind.
menu:
  flux_v0_ref:
    name: math.j0
    parent: math
    identifier: math/j0
weight: 101
---

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`math.j0()` returns the order-zero Bessel function of the first 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.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)}))

```

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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 | 0.12150949471274336  | 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   |

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