feat: allow initialization of null integrators

Project.toml

@@ -42,6 +42,7 @@ SparseArrays = "2f01184e-e22b-5df5-ae63-d93ebab69eaf"
 SparseDiffTools = "47a9eef4-7e08-11e9-0b38-333d64bd3804"
 StaticArrayInterface = "0d7ed370-da01-4f52-bd93-41d350b8b718"
 StaticArrays = "90137ffa-7385-5640-81b9-e52037218182"
+SymbolicIndexingInterface = "2efcf032-c050-4f8e-a9bb-153293bab1f5"
 TruncatedStacktraces = "781d530d-4396-4725-bb49-402e4bee1e77"
 
 [compat]
@@ -84,6 +85,7 @@ SparseArrays = "1.9"
 SparseDiffTools = "2.3"
 StaticArrayInterface = "1.2"
 StaticArrays = "1.0"
+SymbolicIndexingInterface = "0.3.16"
 TruncatedStacktraces = "1.2"
 julia = "1.10"
 

src/OrdinaryDiffEq.jl

@@ -64,6 +64,8 @@ using ExponentialUtilities
 
 using NonlinearSolve
 
+using SymbolicIndexingInterface
+
 # Required by temporary fix in not in-place methods with 12+ broadcasts
 # `MVector` is used by Nordsieck forms
 import StaticArrays: SArray, MVector, SVector, @SVector, StaticArray, MMatrix, SA

src/initialize_dae.jl

@@ -71,6 +71,12 @@ function DiffEqBase.initialize_dae!(integrator::ODEIntegrator,
         Val(DiffEqBase.isinplace(integrator.sol.prob)))
 end
 
+function DiffEqBase.initialize_dae!(integrator::DiffEqBase.NullODEIntegrator)
+    _initialize_dae!(integrator, integrator.sol.prob,
+        OverrideInit(),
+        Val(DiffEqBase.isinplace(integrator.sol.prob)))
+end
+
 ## Default algorithms
 
 function _initialize_dae!(integrator, prob::ODEProblem,
@@ -134,19 +140,24 @@ end
 function _initialize_dae!(integrator, prob::Union{ODEProblem, DAEProblem},
         alg::OverrideInit, isinplace::Union{Val{true}, Val{false}})
     initializeprob = prob.f.initializeprob
-
+    prob.f.initializeprob_init!(initializeprob, integrator)
     # If it doesn't have autodiff, assume it comes from symbolic system like ModelingToolkit
     # Since then it's the case of not a DAE but has initializeprob
     # In which case, it should be differentiable
-    isAD = has_autodiff(integrator.alg) ? alg_autodiff(integrator.alg) isa AutoForwardDiff :
-           true
+    isAD = if !isdefined(integrator, :alg)
+        false
+    elseif has_autodiff(integrator.alg)
+        alg_autodiff(integrator.alg) isa AutoForwardDiff
+    else
+       true
+    end
 
     alg = default_nlsolve(alg.nlsolve, isinplace, initializeprob.u0, initializeprob, isAD)
     nlsol = solve(initializeprob, alg)
     if isinplace === Val{true}()
-        integrator.u .= prob.f.initializeprobmap(nlsol)
+        prob.f.initializeprob_update!(integrator, nlsol)
     elseif isinplace === Val{false}()
-        integrator.u = prob.f.initializeprobmap(nlsol)
+        prob.f.initializeprob_update!(integrator, nlsol)
     else
         error("Unreachable reached. Report this error.")
     end