"Adding parameters" example gives error

[natevmp]

Describe the bug 🐞

Running the "Adding parameters" example script of the docs on Julia v1.10.4, with current versions of ModelingToolkit v9.42.0 and MethodOfLines v0.11.5 gives an error on the discretization step.

Minimal Reproducible Example 👇

using ModelingToolkit, MethodOfLines, OrdinaryDiffEq, DomainSets

@parameters t x
@parameters Dn, Dp
@variables u(..) v(..)
Dt = Differential(t)
Dx = Differential(x)
Dxx = Differential(x)^2

eqs  = [Dt(u(t,x)) ~ Dn * Dxx(u(t,x)) + u(t,x)*v(t,x),
        Dt(v(t,x)) ~ Dp * Dxx(v(t,x)) - u(t,x)*v(t,x)]
bcs = [u(0,x) ~ sin(pi*x/2),
       v(0,x) ~ sin(pi*x/2),
       u(t,0) ~ 0.0, Dx(u(t,1)) ~ 0.0,
       v(t,0) ~ 0.0, Dx(v(t,1)) ~ 0.0]

domains = [t ∈ Interval(0.0,1.0),
           x ∈ Interval(0.0,1.0)]

@named pdesys = PDESystem(eqs,bcs,domains,[t,x],[u(t,x),v(t,x)],[Dn=>0.5, Dp=>2])

discretization = MOLFiniteDifference([x=>0.1],t)

prob = discretize(pdesys,discretization) # This gives an ODEProblem since it's time-dependent
# the error occurs on the above line

sol = solve(prob,Tsit5())

discrete_x = sol[x]
discrete_t = sol[t]

solu = sol[u(t, x)]
solv = sol[v(t, x)]

Error & Stacktrace ⚠️

ERROR: MethodError: no method matching hasmetadata(::Pair{Num, Float64}, ::Type{Symbolics.VariableDefaultValue})

Closest candidates are:
  hasmetadata(::Num, ::Any)
   @ Symbolics ~/.julia/packages/Symbolics/rtkf9/src/Symbolics.jl:188
  hasmetadata(::Complex{Num}, ::Any)
   @ Symbolics ~/.julia/packages/Symbolics/rtkf9/src/Symbolics.jl:188
  hasmetadata(::SymbolicUtils.Symbolic, ::Any)
   @ SymbolicUtils ~/.julia/packages/SymbolicUtils/ij6YM/src/types.jl:631

Stacktrace:
 [1] hasdefault(v::Pair{Num, Float64})
   @ ModelingToolkit ~/.julia/packages/ModelingToolkit/5OzIt/src/utils.jl:237
 [2] collect_defaults!
   @ ~/.julia/packages/ModelingToolkit/5OzIt/src/utils.jl:255 [inlined]
 [3] process_variables!(var_to_name::Dict{Any, Any}, defs::Dict{Any, Any}, vars::Vector{Pair{Num, Float64}})
   @ ModelingToolkit ~/.julia/packages/ModelingToolkit/5OzIt/src/utils.jl:248
 [4] ODESystem(deqs::Vector{…}, iv::Num, dvs::Vector{…}, ps::Vector{…}; controls::Vector{…}, observed::Vector{…}, systems::Vector{…}, tspan::Nothing, name::Symbol, default_u0::Dict{…}, default_p::Dict{…}, defaults::Dict{…}, guesses::Dict{…}, initializesystem::Nothing, initialization_eqs::Vector{…}, schedule::Nothing, connector_type::Nothing, preface::Nothing, continuous_events::Nothing, discrete_events::Nothing, parameter_dependencies::Vector{…}, checks::Bool, metadata::MethodOfLines.MOLMetadata{…}, gui_metadata::Nothing, is_dde::Nothing)
   @ ModelingToolkit ~/.julia/packages/ModelingToolkit/5OzIt/src/systems/diffeqs/odesystem.jl:250
 [5] generate_system(disc_state::PDEBase.EquationState, s::MethodOfLines.DiscreteSpace{…}, u0::Vector{…}, tspan::Tuple{…}, metadata::MethodOfLines.MOLMetadata{…}, disc::MOLFiniteDifference{…})
   @ PDEBase ~/.julia/packages/PDEBase/EWM3U/src/discretization_state.jl:40
 [6] symbolic_discretize(pdesys::PDESystem, discretization::MOLFiniteDifference{…})
   @ PDEBase ~/.julia/packages/PDEBase/EWM3U/src/symbolic_discretize.jl:89
 [7] discretize(pdesys::PDESystem, discretization::MOLFiniteDifference{…}; analytic::Nothing, kwargs::@Kwargs{})
   @ PDEBase ~/.julia/packages/PDEBase/EWM3U/src/discretization_state.jl:57
 [8] discretize(pdesys::PDESystem, discretization::MOLFiniteDifference{…})
   @ PDEBase ~/.julia/packages/PDEBase/EWM3U/src/discretization_state.jl:54
 [9] top-level scope
   @ ~/Library/CloudStorage/OneDrive-QueenMary,UniversityofLondon/GitHub/MicroscopicGradientDynamics/test/parameterExample.jl:24
Some type information was truncated. Use `show(err)` to see complete types.

Environment:

• Output of using Pkg; Pkg.status()

Status `~/Library/CloudStorage/OneDrive-QueenMary,UniversityofLondon/GitHub/MicroscopicGradientDynamics/Project.toml`
  [13f3f980] CairoMakie v0.12.13
  [5b8099bc] DomainSets v0.7.14
  [94925ecb] MethodOfLines v0.11.5
  [961ee093] ModelingToolkit v9.42.0
  [1dea7af3] OrdinaryDiffEq v6.89.0

• Output of versioninfo()

Julia Version 1.10.4
Commit 48d4fd48430 (2024-06-04 10:41 UTC)
Build Info:
  Official https://julialang.org/ release
Platform Info:
  OS: macOS (arm64-apple-darwin22.4.0)
  CPU: 8 × Apple M3
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-15.0.7 (ORCJIT, apple-m1)
Threads: 1 default, 0 interactive, 1 GC (on 4 virtual cores)
Environment:
  JULIA_EDITOR = code
  JULIA_NUM_THREADS = 

[sathvikbhagavan]

Hello,

Can you refer to the latest dev docs here - https://docs.sciml.ai/MethodOfLines/dev/tutorials/params/
The issue is

@named pdesys = PDESystem(eqs,bcs,domains,[t,x],[u(t,x),v(t,x)],[Dn=>0.5, Dp=>2])

is not correct. Instead it should be:

@named pdesys = PDESystem(eqs,bcs,domains,[t,x],[u(t,x),v(t,x)],[Dn, Dp]; defaults = Dict(Dn => 0.5, Dp => 2))

which is fixed in master.

Due to the issues in tagbot, stable docs has not been released for new releases.

[natevmp]

Great. Thanks!