# Was "intall0d" intended for any purpose?

**URL:** <https://community.freefem.org/t/was-intall0d-intended-for-any-purpose/2271>\
**Category:** General Discussion\
**Created:** [February 9, 2023, 9:13pm UTC](https://community.freefem.org/t/was-intall0d-intended-for-any-purpose/2271 "2023-02-09T21:13:21Z")\
**Posts on this page:** 7\
**Page:** 1

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**Author:** ![marchywka](https://avatars.discourse-cdn.com/v4/letter/m/ee59a6/32.png) [@marchywka](https://community.freefem.org/u/marchywka)\
**Post date:** [February 9, 2023, 9:13pm UTC](https://community.freefem.org/t/was-intall0d-intended-for-any-purpose/2271/1 "2023-02-09T21:13:21Z")

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I was trying to find a way to just get the matrix for a differential equation ( no integration/ bilinear form ). That is just the matrix of an expression containing various derivatives on some fespace.

I found some things like “int0d” and most recently “intall0d” which  
sounds like what I’m looking for but it is not used anywhere.

```auto
grep -n "intall0d" `find src -type f -name "*"` | grep enum 
src/fflib/problem.hpp:285: enum typeofkind { int2d=0, int1d=1, intalledges=2,intallVFedges=3, int3d = 4, intallfaces= 5,intallVFfaces=6,int0d=7,intall0d=8 } ; //3d

```

I was going to add something like “intzed” for this purpose since I can’t find another way  
to get there. Thanks. Just making some matricies from varf I think I mostly understand  
what is going on and at least for P0 elements things look about right by inspection 🙂

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**Author:** ![frederichecht](https://yyz2.discourse-cdn.com/flex030/user_avatar/community.freefem.org/frederichecht/32/15_2.png) [@frederichecht](https://community.freefem.org/u/frederichecht)\
**Post date:** [February 10, 2023, 10:33am UTC](https://community.freefem.org/t/was-intall0d-intended-for-any-purpose/2271/2 "2023-02-10T10:33:42Z")

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Can you given a small exact of matrix construction, because you need to explain howto convert function in number to build the matrix.

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<div class="post-metadata">

**Author:** ![marchywka](https://avatars.discourse-cdn.com/v4/letter/m/ee59a6/32.png) [@marchywka](https://community.freefem.org/u/marchywka)\
**Post date:** [February 10, 2023, 4:17pm UTC](https://community.freefem.org/t/was-intall0d-intended-for-any-purpose/2271/3 "2023-02-10T16:17:14Z")

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I just wanted to get the matrix representing a discretized differential equation- not the  
variaional integral . I was wondering if that had something to to with support for strong form.  
Thanks.

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<div class="post-metadata">

**Author:** ![frederichecht](https://yyz2.discourse-cdn.com/flex030/user_avatar/community.freefem.org/frederichecht/32/15_2.png) [@frederichecht](https://community.freefem.org/u/frederichecht)\
**Post date:** [February 11, 2023, 5:35pm UTC](https://community.freefem.org/t/was-intall0d-intended-for-any-purpose/2271/4 "2023-02-11T17:35:28Z")

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So you want to make finite difference scheme!

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<div class="post-metadata">

**Author:** ![marchywka](https://avatars.discourse-cdn.com/v4/letter/m/ee59a6/32.png) [@marchywka](https://community.freefem.org/u/marchywka)\
**Post date:** [February 11, 2023, 10:31pm UTC](https://community.freefem.org/t/was-intall0d-intended-for-any-purpose/2271/5 "2023-02-11T22:31:14Z")

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Well, that is intermingled lol. I have a case I’m doing for learning but also a start  
on a practical application. It is just diffusion but with a spatially varying diffusivity  
that depends on the species concentations. In essence, it is like a two component  
glue such as epoxy with one component circulating in an inert state activated  
at a surface. When the activated hardener meets the flue, the diffusivity drops.

Right now I’m doing finite difference along the time axis . And yes I wanted to get  
the depednence of the time derivatives on the contirbutors to the laplacian.  
But, it should be independent of that. That is, you can get a matrix in  
FEM right? Its just now you only support the weak form.

Thanks.

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<div class="post-metadata">

**Author:** ![frederichecht](https://yyz2.discourse-cdn.com/flex030/user_avatar/community.freefem.org/frederichecht/32/15_2.png) [@frederichecht](https://community.freefem.org/u/frederichecht)\
**Post date:** [February 19, 2023, 3:52pm UTC](https://community.freefem.org/t/was-intall0d-intended-for-any-purpose/2271/6 "2023-02-19T15:52:43Z")

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OK, for me the more simple to have the equation and start in 2d. with time,

you have 2 concentrations c1,c2 depending of space and time

and the minimal equation are something like :

d c1/dt - div( k1(c1,c2) grad(c1)) = ???  
d c2/dt - div( k2(c1,c2) grad(c2)) = ???

tHis problem is hard a level of modélisation ,  
I found a thesis on this subject in french : [Modelization of the joint formation phase of a solvent-based adhesive in a porous medium - Archive ouverte HAL](https://theses.hal.science/tel-00005761)

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<div class="post-metadata">

**Author:** ![marchywka](https://avatars.discourse-cdn.com/v4/letter/m/ee59a6/32.png) [@marchywka](https://community.freefem.org/u/marchywka)\
**Post date:** [February 19, 2023, 4:16pm UTC](https://community.freefem.org/t/was-intall0d-intended-for-any-purpose/2271/7 "2023-02-19T16:16:42Z")

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Thanks. yes this is just diffusion. If there is interest and I get most of the  
junk code removed, I can post the code. I realized I may be able to do this  
even with the integration, I’m sure its just something dumb I was missing.