# UndefValError in Julia

**URL:** <https://discourse.julialang.org/t/undefvalerror-in-julia/22867>\
**Category:** General Usage\
**Created:** [April 7, 2019, 9:28am UTC](https://discourse.julialang.org/t/undefvalerror-in-julia/22867 "2019-04-07T09:28:53Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![bsnyh](https://avatars.discourse-cdn.com/v4/letter/b/ce7236/32.png) [@bsnyh](https://discourse.julialang.org/u/bsnyh)\
**Post date:** [April 7, 2019, 9:28am UTC](https://discourse.julialang.org/t/undefvalerror-in-julia/22867/1 "2019-04-07T09:28:53Z")

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```julia
_/ |\ __'_|_|_|\__'_| | Official https://julialang.org/ release
|__/ |

julia> rand(MersenneTwister(0), Dict(1=>2, 3=>4))
ERROR: UndefVarError: MersenneTwister not defined
Stacktrace:
 [1] top-level scope at none:0

```

I thought as basic as “MersenneTwister”, it is built in with Julia already. Can anyone please give me a hint?

---

<div class="post-metadata">

**Author:** ![fredrikekre](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/fredrikekre/32/1688_2.png) [@fredrikekre](https://discourse.julialang.org/u/fredrikekre)\
**Post date:** [April 7, 2019, 9:29am UTC](https://discourse.julialang.org/t/undefvalerror-in-julia/22867/2 "2019-04-07T09:29:44Z")

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`using Random`