Problem with initial conditions

miklavrent · August 3, 2026, 9:27am

Hi,

Just wanted to attract your attention to what seems to be a bug: FESTIM cannot actually take a list of initial conditions. This is raised on github:

github.com/festim-dev/FESTIM

Initial conditions not setting as expected

opened 08:59AM - 03 Aug 26 UTC

rb-atkn

**Describe the bug** In FESTIM docs tutorials section "Initial conditions -> Tem…perature", initial temperatures are set using: model.initial_conditions = [ F.InitialTemperature(value=300, volume=vol) ] however when attempting to assign initial conditions to a heat transfer model, only the attribute "initial_condition" is available, not the plural, which only allows a single initial condition to be set within a single volume, whereas documentation suggests initial conditions can be set in a list for discontinuous problems with multiple volume subdomains. Setting model.initial_conditions does not throw an error despite not actually setting any conditions. **To Reproduce** Steps to reproduce the behaviour: Set e.g. model.initial_conditions = [ F.InitialTemperature(value=temp, volume=vol1), F.InitialTemperature(value=temp, volume=vol2), F.InitialTemperature(value=temp, volume=vol3), ] and print model.u_n.x.array.min(), model.u_n.x.array.max() which will return "0.0 0.0", whereas when using initial_condition returns "temp temp" (i.e. the value of temp, e.g. 300.0 if temp=300.0) Also attempt to set multiple volumes to a single initial condition model.initial_condition = F.InitialTemperature(value=temp, volume=model.volume_subdomains) which will raise an error TypeError("volume must be of type festim.VolumeSubdomain") **Expected behavior** Expected to be able to set initial conditions in a list for multiple volume subdomains using model.initial_conditions = [], as described within "https://festim-workshop.readthedocs.io/en/latest/content/initial_conditions/temperature.html"

Best wishes,

Mikhail

remidm · August 3, 2026, 10:45am

This seems to be only a problem for a heat transfer problem. I’ll look into it.

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Problem with initial conditions

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