feat: add modelingtoolkitize(::NonlinearProblem)

Author: AayushSabharwal

src/ModelingToolkit.jl

@@ -182,6 +182,7 @@ include("modelingtoolkitize/common.jl")
 include("modelingtoolkitize/odeproblem.jl")
 include("modelingtoolkitize/sdeproblem.jl")
 include("modelingtoolkitize/optimizationproblem.jl")
+include("modelingtoolkitize/nonlinearproblem.jl")
 
 include("systems/nonlinear/homotopy_continuation.jl")
 include("systems/nonlinear/initializesystem.jl")

src/modelingtoolkitize/nonlinearproblem.jl

@@ -0,0 +1,48 @@
+"""
+    $(TYPEDSIGNATURES)
+
+Convert a `NonlinearProblem` or `NonlinearLeastSquaresProblem` to a
+`ModelingToolkit.System`.
+
+# Keyword arguments
+
+- `u_names`: An array of names of the same size as `prob.u0` to use as the names of the
+  unknowns of the system. The names should be given as `Symbol`s.
+- `p_names`: A collection of names to use for parameters of the system. The collection
+  should have keys corresponding to indexes of `prob.p`. For example, if `prob.p` is an
+  associative container like `NamedTuple`, then `p_names` should map keys of `prob.p` to
+  the name that the corresponding parameter should have in the returned system. The names
+  should be given as `Symbol`s.
+
+All other keyword arguments are forwarded to the created `System`.
+"""
+function modelingtoolkitize(
+        prob::Union{NonlinearProblem, NonlinearLeastSquaresProblem};
+        u_names = nothing, p_names = nothing, kwargs...)
+    p = prob.p
+    has_p = !(p isa Union{DiffEqBase.NullParameters, Nothing})
+
+    vars = construct_vars(prob, nothing, u_names)
+    params = construct_params(prob, nothing, p_names)
+
+    rhs = trace_rhs(prob, vars, params, nothing)
+    eqs = vcat([0 ~ rhs[i] for i in eachindex(prob.u0)]...)
+
+    sts = vec(collect(vars))
+
+    # turn `params` into a list of symbolic variables as opposed to
+    # a parameter object containing symbolic variables.
+    _params = params
+    params = vec(collect(values(params)))
+
+    defaults = defaults_from_u0_p(prob, vars, _params, params)
+    # In case initials crept in, specifically from when we constructed parameters
+    # using prob.f.sys
+    filter!(x -> !iscall(x) || !(operation(x) isa Initial), params)
+    filter!(x -> !iscall(x[1]) || !(operation(x[1]) isa Initial), defaults)
+
+    return System(eqs, sts, params;
+        defaults,
+        name = gensym(:MTKizedNonlin),
+        kwargs...)
+end