---
title: math.y1() function
description: >
  `math.y1()` returns the order-one Bessel function of the second kind.
menu:
  flux_v0_ref:
    name: math.y1
    parent: math
    identifier: math/y1
weight: 101
---

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`math.y1()` returns the order-one 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-one Bessel function of a value](#return-the-order-one-bessel-function-of-a-value)
- [Use math.y1 in map](#use-mathy1-in-map)

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

```js
import "math"

math.y1(x: 3.14)// 0.35853138083924085


```


### Use math.y1 in map

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

sampledata.float()
    |> map(fn: (r) => ({r with _value: math.y1(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 | 0.17792152059156155 | t1   |
| 2021-01-01T00:00:20Z | -0.279177585983904  | t1   |
| 2021-01-01T00:00:30Z | 0.09355230538878848 | t1   |
| 2021-01-01T00:00:40Z | 0.06669358775929306 | t1   |
| 2021-01-01T00:00:50Z | 0.318734411734819   | t1   |

| _time                | _value               | *tag |
| -------------------- | -------------------- | ---- |
| 2021-01-01T00:00:00Z | -0.17429072159140693 | t2   |
| 2021-01-01T00:00:10Z | 0.15797094698544048  | t2   |
| 2021-01-01T00:00:20Z | NaN                  | t2   |
| 2021-01-01T00:00:30Z | -0.17740857181789169 | t2   |
| 2021-01-01T00:00:40Z | -0.18452518993372807 | t2   |
| 2021-01-01T00:00:50Z | -0.18788912184316153 | t2   |

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