Merge pull request #1532 from SciML/myb/param

Allow coefficients to be parameters

Author: YingboMa

src/structural_transformation/utils.jl

@@ -173,7 +173,7 @@ function find_eq_solvables!(state::TearingState, ieq; may_be_zero=false, allow_s
         if a isa Symbolic
             if !allow_symbolic
                 if allow_parameter
-                    ModelingToolkit.isparameter(a) || continue
+                    all(ModelingToolkit.isparameter, vars(a)) || continue
                 else
                     continue
                 end

test/odesystem.jl

@@ -657,3 +657,18 @@ let
     @parameters N
     @test_throws Any @named tmp = ODESystem([s + I + r ~ N])
 end
+
+let
+    @parameters C L R
+    @variables t q(t) p(t) F(t)
+    D = Differential(t)
+
+    eqs = [
+           D(q) ~ -p/L - F
+           D(p) ~ q/C
+           0 ~ q/C - R*F
+          ]
+
+    @named sys = ODESystem(eqs, t)
+    @test length(equations(structural_simplify(sys))) == 2
+end