# CallWithMetadata has no field val error for simple PDE system in ModelingToolkit

Hi

``````using DifferentialEquations
using ModelingToolkit, MethodOfLines

@parameters x
@variables t c(..)

Dx = Differential(x)
Dxx = Differential(x)^2
Dt = Differential(t)

L = 1.
D = 0.16
k = 1.
j0 = 0.4

eq  = Dt(c(t,x)) ~ D*Dxx(c(t,x)) - k*c(t,x)

# Initial and boundary conditions
bcs = [c(0,x) ~ 0.,
Dx(c(t,0)) ~ -j0, Dx(c(t,L)) ~ 0.]

# Space and time domains
domains = [t ∈ (0.0,12.0),
x ∈ (0.0,L)]

@named pde_system = PDESystem(eq,bcs,domains,[t,x],[c])

dx = 0.01
order = 2
discretization = MOLFiniteDifference([x => dx], t)

prob = discretize(pde_system,discretization)
``````

produces the error

``````type CallWithMetadata has no field val

Stacktrace:
[1] getproperty
@ ./Base.jl:38 [inlined]
@ MethodOfLines ~/.julia/packages/MethodOfLines/EqHjt/src/MOL_discretization.jl:16
[3] iterate
@ ./generator.jl:47 [inlined]
[4] _collect
@ ./array.jl:807 [inlined]
@ Base ./array.jl:716
[6] map(f::Function, A::Vector{Symbolics.CallWithMetadata{SymbolicUtils.FnType{Tuple, Real}, Base.ImmutableDict{DataType, Any}}})
@ Base ./abstractarray.jl:2933
[7] symbolic_discretize(pdesys::PDESystem, discretization::MOLFiniteDifference{MethodOfLines.CenterAlignedGrid})
@ MethodOfLines ~/.julia/packages/MethodOfLines/EqHjt/src/MOL_discretization.jl:16
[8] discretize(pdesys::PDESystem, discretization::MOLFiniteDifference{MethodOfLines.CenterAlignedGrid})
@ MethodOfLines ~/.julia/packages/MethodOfLines/EqHjt/src/MOL_discretization.jl:162
[9] top-level scope
``````

Project.toml:

``````  [6e4b80f9] BenchmarkTools v1.3.1
[2b5f629d] DiffEqBase v6.105.1
[ebbdde9d] DiffEqBayes v3.1.0
[459566f4] DiffEqCallbacks v2.24.2
[1130ab10] DiffEqParamEstim v1.27.0
[0c46a032] DifferentialEquations v7.5.0
[634d3b9d] DrWatson v2.11.1
[94925ecb] MethodOfLines v0.5.1
⌃ [961ee093] ModelingToolkit v8.29.0
[76087f3c] NLopt v0.6.5
⌃ [91a5bcdd] Plots v1.35.4
[731186ca] RecursiveArrayTools v2.32.0
[0c5d862f] Symbolics v4.13.0
[fce5fe82] Turing v0.21.12
[e88e6eb3] Zygote v0.6.49
[37e2e46d] LinearAlgebra
``````

Any ideas?

Open an issue on the repo.

done