# Using flat() in LinearInterpolation

**URL:** <https://discourse.julialang.org/t/using-flat-in-linearinterpolation/58740>\
**Category:** Numerics\
**Tags:** interpolations\
**Created:** [April 7, 2021, 9:05am UTC](https://discourse.julialang.org/t/using-flat-in-linearinterpolation/58740 "2021-04-07T09:05:16Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![bojeryd91](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/bojeryd91/32/42622_2.png) [@bojeryd91](https://discourse.julialang.org/u/bojeryd91)\
**Post date:** [April 7, 2021, 9:05am UTC](https://discourse.julialang.org/t/using-flat-in-linearinterpolation/58740/1 "2021-04-07T09:05:16Z")

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I want to create an interpolation object which uses the Flat() option when extrapolating, but I run into “Flat() not defined” when specifying it so. The Line() option works well.

Eg., the following works  
interp1 = LinearInterpolation(1:5, 2:6, extrapolation\_bc=Line())  
interp1(6.0) returns 7.0

while  
interp2 = LinearInterpolation(1:5, 2:6, extrapolation\_bc=Flat())  
returns **ERROR: UndefVarError: Flat not defined**

Is this a bug or am I using the option wrong?

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**Author:** ![fgerick](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/fgerick/32/13228_2.png) [@fgerick](https://discourse.julialang.org/u/fgerick)\
**Post date:** [April 7, 2021, 11:13am UTC](https://discourse.julialang.org/t/using-flat-in-linearinterpolation/58740/2 "2021-04-07T11:13:10Z")

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works fine for me on Julia v1.6.0 with `Interpolations v0.13.1`

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<div class="post-metadata">

**Author:** ![bojeryd91](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/bojeryd91/32/42622_2.png) [@bojeryd91](https://discourse.julialang.org/u/bojeryd91)\
**Post date:** [April 7, 2021, 12:24pm UTC](https://discourse.julialang.org/t/using-flat-in-linearinterpolation/58740/3 "2021-04-07T12:24:42Z")

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Ah, updating just Interpolations (still running Julia v1.5.2.) and restarting solved it, thanks!¨

Lesson learned: Update packages before asking.

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**Author:** ![nick-cao](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/nick-cao/32/210553_2.png) [@nick-cao](https://discourse.julialang.org/u/nick-cao)\
**Post date:** [August 31, 2024, 1:50am UTC](https://discourse.julialang.org/t/using-flat-in-linearinterpolation/58740/4 "2024-08-31T01:50:36Z")

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In case this helps anyone else: I was getting this error message too. It turns out that if you have Optim.jl loaded, it also exports Flat(), so you need to specify `extrapolation_bc=Interpolations.Flat()` to use this extrapolation scheme.