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feat: make Pre automatically recurse into subexpressions #4241

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feat: make Pre automatically recurse into subexpressions #4241

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49 changes: 22 additions & 27 deletions lib/ModelingToolkitBase/src/systems/callbacks.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -217,34 +217,29 @@ unPre(x::Symbolics.Arr) = unPre(unwrap(x))
unPre(x::SymbolicT) = (iscall(x) && operation(x) isa Pre) ? only(arguments(x)) : x
distribute_shift_into_operator(::Pre) = false

function (p::Pre)(x)
iw = Symbolics.iswrapped(x)
x = unwrap(x)
# non-symbolic values don't change
SU.isconst(x) && return x
if symbolic_type(x) == NotSymbolic()
return x
end
# differential variables are default-toterm-ed
if iscall(x) && operation(x) isa Differential
x = default_toterm(x)
end
# don't double wrap
iscall(x) && operation(x) isa Pre && return x
result = if iscall(x) && operation(x) === getindex
# instead of `Pre(x[1])` create `Pre(x)[1]`
# which allows parameter indexing to handle this case automatically.
arr = arguments(x)[1]
p(arr)[arguments(x)[2:end]...]
else
term(p, x; type = symtype(x), shape = SU.shape(x))
end
# the result should be a parameter
result = toparam(result)
if iw
result = wrap(result)
(p::Pre)(x::Num) = Num(p(unwrap(x)))
(p::Pre)(x::Symbolics.Arr{T, N}) where {T, N} = Symbolics.Arr{T, N}(p(unwrap(x)))
function (p::Pre)(x::SymbolicT)
iscall(x) || return x
return Moshi.Match.@match x begin
BSImpl.Term(; f) && if f isa Pre end => return x
BSImpl.Term(; f) && if f isa Differential end => begin
return p(default_toterm(x))
end
BSImpl.Term(; f, args, type, shape) && if f === getindex end => begin
newargs = copy(parent(args))
newargs[1] = p(args[1])
return toparam(BSImpl.Term{VartypeT}(f, newargs; type, shape))
end
BSImpl.Term(; f, type, shape) && if f isa SymbolicT && !SU.is_function_symbolic(f) end => begin
return toparam(BSImpl.Term{VartypeT}(p, SArgsT((x,)); type, shape))
end
_ => begin
op = operation(x)
args = map(p, arguments(x))
return toparam(maketerm(SymbolicT, op, args, nothing; type = symtype(x)))
end
end
return result
end
haspre(eq::Equation) = haspre(eq.lhs) || haspre(eq.rhs)
haspre(O) = recursive_hasoperator(Pre, O)
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7 changes: 7 additions & 0 deletions lib/ModelingToolkitBase/test/symbolic_events.jl
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Expand Up @@ -1824,4 +1824,11 @@ if !@isdefined(ModelingToolkit)
@mtkcompile sys = System(eqs, t, [X], [p, Kᵢ, Kₐ, K]; discrete_events)
@test_nowarn ODEProblem(sys, [X => 1, p => 1, Kᵢ => 1, Kₐ => 2], (0.0, 1.0))
end

@testset "Issue:4095: `Pre` recurses into expressions" begin
@variables x(t)
@parameters p (f::Function)(..)
@discretes d(t)
@test isequal(Pre(2x^2 + 3sin(f(x)) - ifelse(p < 0, d, d + 2) + 2p), 2Pre(x)^2 + 3sin(f(Pre(x))) - ifelse(p < 0, Pre(d), Pre(d) + 2) + 2p)
end
end
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