Hello,

I am trying to use MOLFiniteDifference() to solve a stationary PDE. In the documentation, it says that the continuous or time variable is optional, but I couldn’t find any examples of someone using it for a steady state problem. I tried to recreate the documentation example without the time parameter, but I got the following error:

```
MethodError: no method matching DiffEqOperators.MOLFiniteDifference(::Vector{Pair{Symbolics.Num, Float64}}; centered_order=2)
Closest candidates are:
DiffEqOperators.MOLFiniteDifference(::Any, !Matched::Any; upwind_order, centered_order, grid_align) at C:\Users\User\.julia\packages\DiffEqOperators\PH6oI\src\MOLFiniteDifference\MOL_discretization.jl:17
DiffEqOperators.MOLFiniteDifference(::T, !Matched::T2, !Matched::Int64, !Matched::Int64, !Matched::DiffEqOperators.GridAlign) where {T, T2} at C:\Users\User\.julia\packages\DiffEqOperators\PH6oI\src\MOLFiniteDifference\MOL_discretization.jl:9 got unsupported keyword argument "centered_order"
```

This is the code I used to generate this error

```
## 2D Diffusion
begin
# Dependencies
using OrdinaryDiffEq, ModelingToolkit, DiffEqOperators, DomainSets
# Variables, parameters, and derivatives
@parameters x y
@variables u(..)
Dxx = Differential(x)^2
Dyy = Differential(y)^2
# Domain edges
x_min = -2.
x_max = 2.
y_min = -2.
y_max = 2.
#Source term
S(x,y) = x^2 + y^2
# Discretization parameters
dx = 0.1; dy = 0.2
order = 2
# Equation
eq = S(x,y) ~ Dxx(u(x, y)) + Dyy(u(x, y))
# Initial and boundary conditions
bcs = [u(x_min, y) ~ 0,
u(x_max, y) ~ 0,
u(x,y_min) ~ 0,
u(x, y_max) ~ 0]
# Space and time domains
domains = [x ∈ Interval(x_min, x_max),
y ∈ Interval(y_min, y_max)]
# PDE system
@named pdesys = PDESystem([eq], bcs, domains, [x, y], [u(x, y)])
# Method of lines discretization
discretization = MOLFiniteDifference([x=>dx,y=>dy];centered_order=order)
prob = ModelingToolkit.discretize(pdesys,discretization)
# Solution of the ODE system
sol = solve(prob,Tsit5())
end
```

Could someone give me an example of how it should be used for a stationary problem?