---
type: "fhirpath-function"
title: "FHIRPath Function: ln"
function: "ln"
category: "Math"
section: "5.8.5"
source: "fhirpath/functions.json"
---
# FHIRPath Function: ln
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Returns the natural logarithm of the input (i.e. the logarithm base _e_).
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Accepts Decimal input types. Integer and Long types are also accepted via implicit conversion to Decimal. 
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If the input collection is empty, the result is empty.
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If the input collection contains multiple items, the evaluation of the expression will end and signal an error to the calling environment.
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``` fhirpath
1.ln() // 0.0
1.0.ln() // 0.0
```
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## Summary
- **Category**: Math
- **Section**: `5.8.5`
- **Return Type**: `Decimal`
- **Empty Input Result**: `empty`
- **Errors on Multiple Input**: `true`
## Description
Returns the natural logarithm of the input (i.e. the logarithm base _e_).
## Arguments
- none
## Type Mapping
- `Integer-Decimal`
- `Long-Decimal`
- `Decimal-Decimal`
## Example
```fhirpath
1.ln() // 0.0
1.0.ln() // 0.0
```