throw error only in case of initializationproblem

Author: vyudu

src/systems/problem_utils.jl

@@ -333,9 +333,13 @@ end
 function Base.showerror(io::IO, err::MissingGuessError) 
     println(io, 
             """
-            The problem cannot be initialized without providing an additional numeric \
-            guess to serve as a starting point for solving for the initial state. Please \
-            provide another numeric value to `guesses` in the problem constructor.
+            Unable to resolve numeric guesses for all of the variables in the system. \
+            This may be because your guesses are cyclic.
+
+            In order for the problem to be initialized, all of the variables must have \
+            a numeric value to serve as a starting point for the nonlinear solve. \
+            Please provide one or more additional numeric guesses to `guesses` in \
+            the problem constructor.
 
             This error was thrown because symbolic value $(err.val) was found for variable $(err.sym).
             """)
@@ -358,7 +362,7 @@ Keyword arguments:
   [`missingvars`](@ref) to perform the check.
 - `allow_symbolic` allows the returned array to contain symbolic values. If this is `true`,
   `promotetoconcrete` is set to `false`.
-- `is_initializeprob`: Whether the parent problem is an initialization problem.
+- `is_initializeprob, guesses`: Used to determine whether the system is missing guesses.
 """
 function better_varmap_to_vars(varmap::AbstractDict, vars::Vector;
         tofloat = true, use_union = true, container_type = Array,

test/initial_values.jl

@@ -172,7 +172,7 @@ end
             [p => 2q, q => 3p]; warn_cyclic_dependency = true)
     catch
     end
-    @test_throws ModelingToolkit.UnexpectedSymbolicValueInVarmap ODEProblem(
+    @test_throws ModelingToolkit.MissingGuessError ODEProblem(
         sys, [x => 1, y => 2], (0.0, 1.0), [p => 2q, q => 3p])
 end
 
@@ -199,3 +199,15 @@ end
     @test SciMLBase.successful_retcode(sol)
     @test sol.u[1] ≈ [1.0, 1.0, 0.5, 0.5]
 end
+
+@testset "Missing/cyclic guesses throws error" begin
+    @parameters g
+    @variables x(t) y(t) [state_priority = 10] λ(t)
+    eqs = [D(D(x)) ~ λ * x
+           D(D(y)) ~ λ * y - g
+           x^2 + y^2 ~ 1]
+    @mtkbuild pend = ODESystem(eqs, t)
+
+    @test_throws ModelingToolkit.MissingGuessError ODEProblem(pend, [x => 1], (0, 1), [g => 1], guesses = [y => λ, λ => y + 1])
+    ODEProblem(pend, [x => 1], (0, 1), [g => 1], guesses = [y => λ, λ => 0.5])
+end