# Utilising ffddm

**URL:** <https://community.freefem.org/t/utilising-ffddm/861>\
**Category:** General Discussion\
**Created:** [March 18, 2021, 12:59pm UTC](https://community.freefem.org/t/utilising-ffddm/861 "2021-03-18T12:59:10Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![niaa](https://avatars.discourse-cdn.com/v4/letter/n/278dde/32.png) [@niaa](https://community.freefem.org/u/niaa)\
**Post date:** [March 18, 2021, 12:59pm UTC](https://community.freefem.org/t/utilising-ffddm/861/1 "2021-03-18T12:59:10Z")

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Hello developers,

When I want to use ffddm I get an error " The identifier mpsize doesn’t exist. For using ffddm I have to install a package or add particular library?

I just tried a simple command, but got error.  
ffddmbuildDmesh( M , ThGlobal , mpiCommWorld )

Thanks.

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**Author:** ![LucasPa](https://yyz2.discourse-cdn.com/flex030/user_avatar/community.freefem.org/lucaspa/32/347_2.png) [@LucasPa](https://community.freefem.org/u/LucasPa)\
**Post date:** [March 18, 2021, 3:24pm UTC](https://community.freefem.org/t/utilising-ffddm/861/2 "2021-03-18T15:24:35Z")

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Hi,

How did you lanch your script ? You have to perform a parallel computation with:

`ff-mpirun -np NUMBER_OF_PROCS NAME_OF_YOUR_SCRIPT.edp`

Lucas

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**Author:** ![niaa](https://avatars.discourse-cdn.com/v4/letter/n/278dde/32.png) [@niaa](https://community.freefem.org/u/niaa)\
**Post date:** [March 18, 2021, 3:51pm UTC](https://community.freefem.org/t/utilising-ffddm/861/3 "2021-03-18T15:51:59Z")

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I was just compiling it without any parallel computation. I am new and dont know how to do it.  
So as an example I have to add this section in a script test.edp:

“macro dimension 2// EOM // 2D or 3D  
include “ffddm.idp”  
mesh ThGlobal = square(100,100); // global mesh  
// Step 1: Decompose the mesh  
ffddmbuildDmesh( M , ThGlobal , mpiCommWorld )  
medit(“Th”+mpirank, MThi);”

and this “ff-mpirun -np 2 test.edp” in another script?

Thanks.  
Niaa

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**Author:** ![prj](https://avatars.discourse-cdn.com/v4/letter/p/ecae2f/32.png) [@prj](https://community.freefem.org/u/prj)\
**Post date:** [March 18, 2021, 4:17pm UTC](https://community.freefem.org/t/utilising-ffddm/861/4 "2021-03-18T16:17:59Z")

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If you are new to parallel computing with FreeFEM, you may be interested in these two tutorial videos: [[1](https://www.youtube.com/watch?v=-Aw2O46V2bo), [2](https://www.youtube.com/watch?v=Hx57gxTOnvE)].

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**Author:** ![niaa](https://avatars.discourse-cdn.com/v4/letter/n/278dde/32.png) [@niaa](https://community.freefem.org/u/niaa)\
**Post date:** [March 18, 2021, 4:57pm UTC](https://community.freefem.org/t/utilising-ffddm/861/5 "2021-03-18T16:57:58Z")

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Too helpful, thanks alot.