This section covers some of the more advanced syntax and features for building chemical reaction network models (still not very complicated!).
The reaction network DSL can "see" user defined functions that work with ModelingToolkit. E.g., this is should work
myHill(x) = 2.0*x^3/(x^3+1.5^3) rn = @reaction_network begin myHill(X), ∅ → X end
In some cases, it may be necessary or desirable to register functions with ModelingToolkit before their use in Catalyst, see the discussion here.
While generally one wants the reaction rate to use the law of mass action, so the reaction
rn = @reaction_network begin k, X → ∅ end k
occurs at the rate $d[X]/dt = -k[X]$, it is possible to ignore this by using any of the following non-filled arrows when declaring the reaction:
⟺. This means that the reaction
rn = @reaction_network begin k, X ⇒ ∅ end k
will occur at rate $d[X]/dt = -k$ (which might become a problem since $[X]$ will be degraded at a constant rate even when very small or equal to 0).