Handle modelingtoolkitize for nonlinearleastsquaresproblem

Fixes #2669

Author: ChrisRackauckas

src/systems/nonlinear/modelingtoolkitize.jl

@@ -4,7 +4,8 @@ $(TYPEDSIGNATURES)
 Generate `NonlinearSystem`, dependent variables, and parameters from an `NonlinearProblem`.
 """
 function modelingtoolkitize(
-        prob::NonlinearProblem; u_names = nothing, p_names = nothing, kwargs...)
+        prob::Union{NonlinearProblem, NonlinearLeastSquaresProblem};
+        u_names = nothing, p_names = nothing, kwargs...)
     p = prob.p
     has_p = !(p isa Union{DiffEqBase.NullParameters, Nothing})
 
@@ -37,13 +38,18 @@ function modelingtoolkitize(
     end
 
     if DiffEqBase.isinplace(prob)
-        rhs = ArrayInterface.restructure(prob.u0, similar(vars, Num))
+        if prob isa NonlinearLeastSquaresProblem
+            rhs = ArrayInterface.restructure(prob.f.resid_prototype, similar(prob.f.resid_prototype, Num))
+        else
+            rhs = ArrayInterface.restructure(prob.u0, similar(vars, Num))
+        end
         prob.f(rhs, vars, params)
+        eqs = vcat([0.0 ~ rhs[i] for i in 1:length(prob.f.resid_prototype)]...)
     else
         rhs = prob.f(vars, params)
+        out_def = prob.f(prob.u0, prob.p)
+        eqs = vcat([0.0 ~ rhs[i] for i in 1:length(out_def)]...)
     end
-    out_def = prob.f(prob.u0, prob.p)
-    eqs = vcat([0.0 ~ rhs[i] for i in 1:length(out_def)]...)
 
     sts = vec(collect(vars))
     _params = params

test/modelingtoolkitize.jl

@@ -473,3 +473,17 @@ sys = modelingtoolkitize(prob)
         end
     end
 end
+
+## NonlinearLeastSquaresProblem
+
+function nlls!(du, u, p)
+    du[1] = 2u[1] - 2
+    du[2] = u[1] - 4u[2]
+    du[3] = 0
+end
+u0 = [0.0, 0.0]
+prob = NonlinearLeastSquaresProblem(
+    NonlinearFunction(nlls!, resid_prototype = zeros(3)), u0)
+sys = modelingtoolkitize(prob)
+@test length(equations(sys)) == 3
+@test length(equations(structural_simplify(sys; fully_determined = false))) == 0