# What is \`Ei\` in SymPy.jl?

**URL:** <https://discourse.julialang.org/t/what-is-ei-in-sympy-jl/114636>\
**Category:** General Usage\
**Tags:** symbolics\
**Created:** [May 23, 2024, 5:41pm UTC](https://discourse.julialang.org/t/what-is-ei-in-sympy-jl/114636 "2024-05-23T17:41:17Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![pgbarletta](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/pgbarletta/32/3204_2.png) [@pgbarletta](https://discourse.julialang.org/u/pgbarletta)\
**Post date:** [May 23, 2024, 5:41pm UTC](https://discourse.julialang.org/t/what-is-ei-in-sympy-jl/114636/1 "2024-05-23T17:41:17Z")

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I tried to get this integral:

```julia
@syms r::real a::real
fff = integrate((1/r)*exp(-2*a*r), (r))

```

and got this:  
 ![image](https://global.discourse-cdn.com/julialang/original/3X/d/d/dd8753aefabe733da214221d81eb9b5345db1a97.png)

what’s that `Ei`?

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<div class="post-metadata">

**Author:** ![stillyslalom](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/stillyslalom/32/45687_2.png) [@stillyslalom](https://discourse.julialang.org/u/stillyslalom)\
**Post date:** [May 23, 2024, 5:51pm UTC](https://discourse.julialang.org/t/what-is-ei-in-sympy-jl/114636/2 "2024-05-23T17:51:16Z")

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The classical exponential integral. [Special - SymPy 1.12.1rc1 documentation](https://docs.sympy.org/latest/modules/functions/special.html#sympy.functions.special.error_functions.Ei)

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<div class="post-metadata">

**Author:** ![pgbarletta](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/pgbarletta/32/3204_2.png) [@pgbarletta](https://discourse.julialang.org/u/pgbarletta)\
**Post date:** [May 23, 2024, 7:18pm UTC](https://discourse.julialang.org/t/what-is-ei-in-sympy-jl/114636/3 "2024-05-23T19:18:06Z")

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Thanks! I’d never seen that before.