> ## Documentation Index
> Fetch the complete documentation index at: https://axiom.co/docs/llms.txt
> Use this file to discover all available pages before exploring further.

<AgentInstructions>

## Submitting Feedback

If you encounter incorrect, outdated, or confusing documentation on this page, submit feedback:

POST https://axiom.co/docs/feedback

```json
{
  "path": "/apl/scalar-functions/mathematical-functions/atan",
  "feedback": "Description of the issue"
}
```

Only submit feedback when you have something specific and actionable to report.

</AgentInstructions>

# atan

> This page explains how to use the atan function in APL.

Use the `atan` function in APL to compute the arc tangent (inverse tangent) of a numeric expression. The function returns the angle, in radians, whose tangent equals the input value. Unlike `asin` and `acos`, `atan` accepts any real number as input.

`atan` is useful when you want to map a numeric value from an unbounded range to a bounded angular range (-π/2, π/2). For example, you can use `atan` to normalize latency deviations, scores, or ratios into a smooth angle scale for comparison or encoding.

## For users of other query languages

If you come from other query languages, this section explains how to adjust your existing queries to achieve the same results in APL.

<AccordionGroup>
  <Accordion title="Splunk SPL users">
    In Splunk SPL, `atan()` is available in the `eval` command with the same behavior: it returns the arc tangent in radians for any real number input.

    <CodeGroup>
      ```sql Splunk example theme={null}
      | eval angle = atan(normalized)
      ```

      ```kusto APL equivalent theme={null}
      ['sample-http-logs']
      | extend angle = atan(normalized)
      ```
    </CodeGroup>
  </Accordion>

  <Accordion title="ANSI SQL users">
    In ANSI SQL, `ATAN()` is a standard mathematical function with identical semantics. It accepts any real number and returns the arc tangent in radians.

    <CodeGroup>
      ```sql SQL example theme={null}
      SELECT ATAN(normalized) AS angle FROM logs
      ```

      ```kusto APL equivalent theme={null}
      ['sample-http-logs']
      | extend angle = atan(normalized)
      ```
    </CodeGroup>
  </Accordion>
</AccordionGroup>

## Usage

### Syntax

```kusto theme={null}
atan(x)
```

### Parameters

| Name | Type | Required | Description    |
| ---- | ---- | -------- | -------------- |
| `x`  | real | Yes      | A real number. |

### Returns

The arc tangent of `x` in radians, in the range (-π/2, π/2).

## Example

Use `atan` to compute the arctangent of a value and return the angle in radians.

**Query**

```kusto theme={null}
print result = atan(1)
```

[Run in Playground](https://play.axiom.co/axiom-play-qf1k/query?initForm=%7B%22apl%22%3A%20%22print%20result%20%3D%20atan%281%29%22%7D)

**Output**

| result |
| ------ |
| 0.7854 |

## List of related functions

* [atan2](/apl/scalar-functions/mathematical-functions/atan2): Returns the arc tangent using two arguments (y, x). Use it when you have separate numerator and denominator values.
* [asin](/apl/scalar-functions/mathematical-functions/asin): Returns the arc sine. Use it when the input is bounded to \[-1, 1].
* [acos](/apl/scalar-functions/mathematical-functions/acos): Returns the arc cosine. Use it when you need the inverse cosine instead.
* [tan](/apl/scalar-functions/mathematical-functions/tan): Returns the tangent. Use it to apply the forward transformation before using `atan` as the inverse.
* [radians](/apl/scalar-functions/mathematical-functions/radians): Converts degrees to radians. Use it when your angle data is in degrees.