Frequently Asked Questions

Getting the index for a symbol

Since ordering of symbols is not guaranteed after symbolic transformations, one should normally refer to values by their name. For example, sol[lorenz.x] from the solution. But what if you need to get the index? The following helper function will do the trick:

indexof(sym,syms) = findfirst(isequal(sym),syms)
indexof(σ,parameters(sys))

Transforming value maps to arrays

ModelingToolkit.jl allows (and recommends) input maps like [x => 2.0, y => 3.0] because symbol ordering is not guaranteed. However, what if you want to get the lowered array? You can use the internal function varmap_to_vars. For example:

pnew = varmap_to_vars([β=>3.0, c=>10.0, γ=>2.0],parameters(sys))