ModelingToolkit.jl Examples

modelingtoolkit_examples.md

Expression substitution

# suggested on Slack (20/01/2020)

using ModelingToolkit
using MacroTools: postwalk

function replace(ex::ModelingToolkit.Expression, ps::Pair...)
    d = Dict(ps...)
    expr = postwalk(Expr(ex)) do x
        get(d, x, x)
    end
    eval(expr)
end

julia> @variables C, x
(C, x)
julia> replace(4 * (C + 1)/x, :C => 1)
8 / x

# Note: it would be preferable to to define a postwalk on Expression 
# instead of Expr and then do the replacements directly on the Expression. 
# This is not straightforward though, since ModelingToolkit.Variables are treated like function calls.