fix: fix remake not able to substitute values

src/remake.jl

@@ -1072,10 +1072,20 @@ function _updated_u0_p_symmap(prob, u0, ::Val{true}, p, ::Val{true}, t0)
         varmap[only(independent_variable_symbols(prob))] = t0
     end
     for (k, v) in u0
-        u0[k] = symbolic_type(v) === NotSymbolic() ? v : symbolic_evaluate(v, varmap)
+        v = symbolic_type(v) === NotSymbolic() ? v : symbolic_evaluate(v, varmap)
+        # if `symbolic_evaluate` can't get us a concrete value,
+        # use the old one from `prob`.
+        if symbolic_type(v) != NotSymbolic()
+            v = getu(prob, k)(prob)
+        end
+        u0[k] = v
     end
     for (k, v) in p
-        p[k] = symbolic_type(v) === NotSymbolic() ? v : symbolic_evaluate(v, varmap)
+        v = symbolic_type(v) === NotSymbolic() ? v : symbolic_evaluate(v, varmap)
+        if symbolic_type(v) != NotSymbolic()
+            v = getu(prob, k)(prob)
+        end
+        p[k] = v
     end
     return remake_buffer(prob, state_values(prob), keys(u0), values(u0)),
     remake_buffer(prob, parameter_values(prob), keys(p), values(p))

test/downstream/modelingtoolkit_remake.jl

@@ -380,3 +380,20 @@ end
         @test prob2.ps[p] ≈ 3.0
     end
 end
+
+# https://github.com/SciML/ModelingToolkit.jl/issues/3326
+@testset "Remake with non-substitute-able values" begin
+    @variables x1(t) x2(t) y(t)
+    @parameters k2 p Gamma y0 d k1
+    @mtkbuild sys = ODESystem([D(y) ~ p - d * y, D(x1) ~ -k1 * x1 + k2 * (Gamma - x1), x2 ~ Gamma - x1], t; defaults = Dict(y => y0, Gamma => x1 + x2))
+    u0 = [x1 => 1.0, x2 => 2.0]
+    p0 = [p => 10.0, d => 5.0, y0 => 3.0, k1 => 1.0, k2 => 2.0]
+    prob = ODEProblem(sys, u0, (0.0, 1.0), p0)
+    u0_new = [x1 => 0.1]
+    ps_new = [y0 => 0.3, p => 100.0]
+    prob2 = remake(prob; u0 = u0_new, p = ps_new)
+    @test prob2[x1] ≈ 0.1
+    @test prob2[y] ≈ 0.3
+    # old value retained
+    @test prob2.ps[Gamma] ≈ 3.0
+end