Params have been made immutable through the back door

When we designed the parametere struct stuff, the idea was to allow the addition of parameters during simulations.

However, for Simulations using boxing, this was never actually possible, since the boxing interface, needs to know the interactionlength at init time. Thus, adding "larger" particles later in the simulation could potentially fail dramatically.

Possible mitigations

• reinit grid everytime params are updated
• drop interactionrange and just let the user manually specify the box grid size on calling evolve!
• ?

tagging @jisense for feedback