# Setting initial H concentration

**URL:** <https://festim.discourse.group/t/setting-initial-h-concentration/90>\
**Category:** User Support\
**Created:** [December 12, 2024, 10:45pm UTC](https://festim.discourse.group/t/setting-initial-h-concentration/90 "2024-12-12T22:45:07Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![HelenS](https://avatars.discourse-cdn.com/v4/letter/h/90ced4/32.png) [@HelenS](https://festim.discourse.group/u/HelenS)\
**Post date:** [December 12, 2024, 10:45pm UTC](https://festim.discourse.group/t/setting-initial-h-concentration/90/1 "2024-12-12T22:45:07Z")

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I’m afraid I’m a little confused again about sources and initial conditions. I can now use ‘sources’, that introduce some H/m3/s (so the total H continually increases throughout the simulation). I now want to put in just an amount of H in volume 1 at the start of the simulation (and see it migrate during the simulation til equilibrium is reached).  
I’ve read everything on initial conditions:

My\_model.initial\_conditions = F. InitialCondition(Field=0, value =10)

But I can’t find an example of the syntax to make my model run with that initial condition, or how I can put H in solution initial values into the different volumes. Is that feasible, please?

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<div class="post-metadata">

**Author:** ![VVKulagin](https://yyz2.discourse-cdn.com/free1/user_avatar/festim.discourse.group/vvkulagin/32/51_2.png) [@VVKulagin](https://festim.discourse.group/u/VVKulagin)\
**Post date:** [December 12, 2024, 11:14pm UTC](https://festim.discourse.group/t/setting-initial-h-concentration/90/2 "2024-12-12T23:14:23Z")

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Hi @HelenS!

You can set the initial concentration in a specific domain with `sympy.Piecewise(...)` function:

```auto
my_model.initial_conditions = [
    F.InitialCondition(field=0, value=10*sympy.Piecewise((1, F.x <= L), (0, True))),
]

```

where `L` is the length of the first domain, for example. See [this topic](https://festim.discourse.group/t/multi-material-problem-initial-trap-distribution-and-diffusion-barrier/71) for additional details.

Please, let me know if it is what you’ve asked about.

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<div class="post-metadata">

**Author:** ![remidm](https://yyz2.discourse-cdn.com/free1/user_avatar/festim.discourse.group/remidm/32/4_2.png) [@remidm](https://festim.discourse.group/u/remidm)\
**Post date:** [December 13, 2024, 2:33am UTC](https://festim.discourse.group/t/setting-initial-h-concentration/90/3 "2024-12-13T02:33:59Z")

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Hi @HelenS you can find a example in the [pre-loaded slab verification case](https://festim-vv-report.readthedocs.io/en/latest/verification/mes/tmap_1c.html) where the initial concentration in x=[0, 10] is set to 1 and then diffuses:

 ![image](https://global.discourse-cdn.com/free1/uploads/festim/original/1X/8a2a9e71ae7e22c441c8a4a67997210b230fea6c.png)

This is the part of the code for the initial condition:

```python
initial_concentration = sp.Piecewise((C_0, F.x <= preloaded_length), (0, True))
model.initial_conditions = [
    F.InitialCondition(field="solute", value=initial_concentration)
]

```