---
type: "fhirpath-function"
title: "FHIRPath Function: exp"
function: "exp"
category: "Math"
section: "5.8.3"
source: "fhirpath/functions.json"
---
# FHIRPath Function: exp
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Returns _e_ raised to the power of the input.
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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
0.exp() // 1.0
(-0.0).exp() // 1.0
```
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## Summary
- **Category**: Math
- **Section**: `5.8.3`
- **Return Type**: `Decimal`
- **Empty Input Result**: `empty`
- **Errors on Multiple Input**: `true`
## Description
Returns _e_ raised to the power of the input.
## Arguments
- none
## Type Mapping
- `Integer-Decimal`
- `Long-Decimal`
- `Decimal-Decimal`
## Example
```fhirpath
0.exp() // 1.0
(-0.0).exp() // 1.0
```