# Documentation

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# expint

Exponential integral

## Syntax

`Y = expint(X)`

## Description

`Y = expint(X)` evaluates the exponential integral for each element of `X`.

## More About

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### Exponential Integral

The exponential integral computed by this function is defined as

Another common definition of the exponential integral function is the Cauchy principal value integral

which, for real positive x, is related to `expint` as

`${E}_{1}\left(-x\right)=-\text{Ei}\left(x\right)-i\pi$`

## References

[1] Abramowitz, M. and I. A. Stegun. Handbook of Mathematical Functions. Chapter 5, New York: Dover Publications, 1965.

## Extended Capabilities

### C/C++ Code GenerationGenerate C and C++ code using MATLAB® Coder™.

#### Introduced before R2006a

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