# `ln`

## Description

Computes the natural logarithm (base *e*) of a number.

## Syntax

Like many functions in DataPrime, `ln` supports [two notations](https://coralogix.com/docs/dataprime/language-reference/functions-reference/index.md), **function** and **method** notation. These interchangeable forms allow flexibility in how you structure expressions.

```dataprime
ln(number: number): number
```

```dataprime
(number: number).ln(): number
```

## Arguments

| Name   | Type   | Required | Description                                         |
| ------ | ------ | -------- | --------------------------------------------------- |
| number | number | **true** | The number whose natural logarithm will be computed |

## Example

**Use case: Model exponential growth with Euler's number and natural logarithm**

Calculate the growth rate from observed data, then project future values using `e` and `ln`.

### Example data

```json
{
    "initial_value": 500,
    "current_value": 1000,
    "time_since_start_hours": 10
}
```

### Example query

```dataprime
create growth_rate from ((1 / time_since_start_hours) * (ln(current_value / initial_value)))
```

```dataprime
create growth_rate from ((1 / time_since_start_hours) * ((current_value / initial_value).ln()))
```

### Example output

```json
{
    "initial_value": 500,
    "current_value": 1000,
    "time_since_start_hours": 10,
    "growth_rate": 0.0693,
    "prediction_in_ten_hours": 1999.41
}
```