# Doubt in the 7 - Gridap Darcy Equation Tutorial

**URL:** https://discourse.julialang.org/t/doubt-in-the-7-gridap-darcy-equation-tutorial/106673
**Category:** New to Julia
**Tags:** question
**Created:** [November 24, 2023, 11:14am UTC](https://discourse.julialang.org/t/doubt-in-the-7-gridap-darcy-equation-tutorial/106673 "2023-11-24T11:14:46Z")
**Posts on this page:** 2
**Page:** 1

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### Author: ![pablorubial](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/pablorubial/32/204055_2.png) [@pablorubial](https://discourse.julialang.org/u/pablorubial)
#### Post date: [November 24, 2023, 11:14am UTC](https://discourse.julialang.org/t/doubt-in-the-7-gridap-darcy-equation-tutorial/106673/1 "2023-11-24T11:14:46Z")

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Hi everyone,

I’m new on Julia and I have two doubts about how Julian works:

In this tutorial a function is defined to define differents properties in different parts of the domain:

function σ(x,u)  
if ((abs(x[1]-0.5) \<= 0.1) && (abs(x[2]-0.5) \<= 0.1))  
return kinv2⋅u  
else  
return kinv1⋅u  
end  
end

I don’t understand why then in the bilinear form the following composition is needed to use this function:  
σ∘(px,u)  
What sense have this composing?

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<div class="post-metadata">

### Author: ![mkitti](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mkitti/32/12459_2.png) [@mkitti](https://discourse.julialang.org/u/mkitti)
#### Post date: [November 24, 2023, 6:10pm UTC](https://discourse.julialang.org/t/doubt-in-the-7-gridap-darcy-equation-tutorial/106673/2 "2023-11-24T18:10:59Z")

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Could you link the tutorial?