---
title: math.ldexp() function
description: math.ldexp() is the inverse of math.frexp(). It returns frac x 2**exp.
url: https://docs.influxdata.com/flux/v0/stdlib/math/ldexp/
estimated_tokens: 1541
product: Flux
version: v0
---

# math.ldexp() function

-   Flux 0.22.0+
-   View InfluxDB support

`math.ldexp()` is the inverse of `math.frexp()`. It returns `frac x 2**exp`.

##### Function type signature

```js
(exp: int, frac: float) => float
```

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

## Parameters

### frac

(Required) Fraction to use in the operation.

### exp

(Required) Exponent to use in the operation.

## Examples

-   [Return the inverse of math.frexp](#return-the-inverse-of-mathfrexp)
-   [Use math.ldexp in map](#use-mathldexp-in-map)

### Return the inverse of math.frexp

```js
import "math"

math.ldexp(frac: 0.5, exp: 6)// 32.0

```

### Use math.ldexp in map

```js
import "math"

data
    |> map(fn: (r) => ({_time: r._time, tag: r.tag, _value: math.ldexp(frac: r.frac, exp: r.exp)}))
```

[](#view-example-input-and-output)

View example input and output

#### Input data

| *tag | _time | exp | frac |
| --- | --- | --- | --- |
| t1 | 2021-01-01T00:00:00Z | 2 | -0.545 |
| t1 | 2021-01-01T00:00:10Z | 4 | 0.6825 |
| t1 | 2021-01-01T00:00:20Z | 3 | 0.91875 |
| t1 | 2021-01-01T00:00:30Z | 5 | 0.5478125 |
| t1 | 2021-01-01T00:00:40Z | 4 | 0.951875 |
| t1 | 2021-01-01T00:00:50Z | 3 | 0.55375 |

| *tag | _time | exp | frac |
| --- | --- | --- | --- |
| t2 | 2021-01-01T00:00:00Z | 5 | 0.6203125 |
| t2 | 2021-01-01T00:00:10Z | 3 | 0.62125 |
| t2 | 2021-01-01T00:00:20Z | 2 | -0.9375 |
| t2 | 2021-01-01T00:00:30Z | 5 | 0.6178125 |
| t2 | 2021-01-01T00:00:40Z | 4 | 0.86625 |
| t2 | 2021-01-01T00:00:50Z | 1 | 0.93 |

#### Output data

| _time | _value | *tag |
| --- | --- | --- |
| 2021-01-01T00:00:00Z | -2.18 | t1 |
| 2021-01-01T00:00:10Z | 10.92 | t1 |
| 2021-01-01T00:00:20Z | 7.35 | t1 |
| 2021-01-01T00:00:30Z | 17.53 | t1 |
| 2021-01-01T00:00:40Z | 15.23 | t1 |
| 2021-01-01T00:00:50Z | 4.43 | t1 |

| _time | _value | *tag |
| --- | --- | --- |
| 2021-01-01T00:00:00Z | 19.85 | t2 |
| 2021-01-01T00:00:10Z | 4.97 | t2 |
| 2021-01-01T00:00:20Z | -3.75 | t2 |
| 2021-01-01T00:00:30Z | 19.77 | t2 |
| 2021-01-01T00:00:40Z | 13.86 | t2 |
| 2021-01-01T00:00:50Z | 1.86 | t2 |