fix: add better warning for missing guess

src/systems/diffeqs/abstractodesystem.jl

@@ -1504,5 +1504,5 @@ function InitializationProblem{iip, specialize}(sys::AbstractSystem,
     else
         NonlinearLeastSquaresProblem
     end
-    TProb(isys, u0map, parammap; kwargs..., build_initializeprob = false)
+    TProb(isys, u0map, parammap; kwargs..., build_initializeprob = false, is_initializeprob = true)
 end

src/systems/problem_utils.jl

@@ -325,6 +325,22 @@ function Base.showerror(io::IO, err::UnexpectedSymbolicValueInVarmap)
         """)
 end
 
+struct MissingGuessError <: Exception
+    sym::Any
+    val::Any
+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.
+
+            This error was thrown because symbolic value $(err.val) was found for variable $(err.sym).
+            """)
+end
+
 """
     $(TYPEDSIGNATURES)
 
@@ -342,10 +358,11 @@ 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.
 """
 function better_varmap_to_vars(varmap::AbstractDict, vars::Vector;
         tofloat = true, use_union = true, container_type = Array,
-        toterm = default_toterm, promotetoconcrete = nothing, check = true, allow_symbolic = false)
+        toterm = default_toterm, promotetoconcrete = nothing, check = true, allow_symbolic = false, is_initializeprob = false)
     isempty(vars) && return nothing
 
     if check
@@ -356,7 +373,11 @@ function better_varmap_to_vars(varmap::AbstractDict, vars::Vector;
     if !allow_symbolic
         for (sym, val) in zip(vars, vals)
             symbolic_type(val) == NotSymbolic() && continue
-            throw(UnexpectedSymbolicValueInVarmap(sym, val))
+            if is_initializeprob
+                throw(MissingGuessError(sym, val))
+            else
+                throw(UnexpectedSymbolicValueInVarmap(sym, val))
+            end
         end
     end
 
@@ -704,7 +725,7 @@ Keyword arguments:
 - `fully_determined`: Override whether the initialization system is fully determined.
 - `check_initialization_units`: Enable or disable unit checks when constructing the
   initialization problem.
-- `tofloat`, `use_union`: Passed to [`better_varmap_to_vars`](@ref) for building `u0` (and
+- `tofloat`, `use_union`, `is_initializeprob`: Passed to [`better_varmap_to_vars`](@ref) for building `u0` (and
   possibly `p`).
 - `u0_constructor`: A function to apply to the `u0` value returned from `better_varmap_to_vars`
   to construct the final `u0` value.
@@ -742,7 +763,7 @@ function process_SciMLProblem(
         circular_dependency_max_cycles = 10,
         substitution_limit = 100, use_scc = true,
         force_initialization_time_independent = false, algebraic_only = false,
-        allow_incomplete = false, kwargs...)
+        allow_incomplete = false, is_initializeprob = false, kwargs...)
     dvs = unknowns(sys)
     ps = parameters(sys; initial_parameters = true)
     iv = has_iv(sys) ? get_iv(sys) : nothing
@@ -815,7 +836,7 @@ function process_SciMLProblem(
 
     u0 = better_varmap_to_vars(
         op, dvs; tofloat = true, use_union = false,
-        container_type = u0Type, allow_symbolic = symbolic_u0)
+        container_type = u0Type, allow_symbolic = symbolic_u0, is_initializeprob)
 
     if u0 !== nothing
         u0 = u0_constructor(u0)

src/variables.jl

@@ -219,7 +219,7 @@ end
 
 function Base.showerror(io::IO, e::MissingVariablesError)
     println(io, MISSING_VARIABLES_MESSAGE)
-    println(io, e.vars)
+    println(io, join(e.vars, ", "))
 end
 
 function _varmap_to_vars(varmap::Dict, varlist; defaults = Dict(), check = false,