MOLFiniteDifference ERROR: TypeError: non-boolean (Term{Bool, Nothing}) used in boolean context

[valentinsulzer]

MOLFiniteDifference is broken (at least locally for me, maybe I am doing something wrong)

Code:

using ModelingToolkit, DiffEqOperators, LinearAlgebra, OrdinaryDiffEq

# Define some variables
@parameters t x
@variables u(..)
Dt = Differential(t)
Dxx = Differential(x)^2
eq  = Dt(u(t,x)) ~ Dxx(u(t,x))
bcs = [u(0,x) ~ - x * (x-1) * sin(x),
       u(t,0) ~ 0.0, u(t,1) ~ 0.0]

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

pdesys = PDESystem(eq,bcs,domains,[t,x],[u(t,x)])
discretization = MOLFiniteDifference([x=>0.1],t)
prob = discretize(pdesys,discretization)

Stacktrace:

ERROR: TypeError: non-boolean (Term{Bool, Nothing}) used in boolean context
Stacktrace:

[1] filter(f::DiffEqOperators.var"#182#215"{Num}, a::Vector{Num})

@ Base ./array.jl:2507

[2] symbolic_discretize(pdesys::PDESystem, discretization::MOLFiniteDifference{Vector{Pair{Num, Float64}}, Num})

@ DiffEqOperators ~/Documents/SciML/DiffEqOperators.jl/src/MOLFiniteDifference/MOL_discretization.jl:17

[3] discretize(pdesys::PDESystem, discretization::MOLFiniteDifference{Vector{Pair{Num, Float64}}, Num})

@ DiffEqOperators ~/Documents/SciML/DiffEqOperators.jl/src/MOLFiniteDifference/MOL_discretization.jl:152

[4] top-level scope

@ ~/Documents/SciML/DiffEqOperators.jl/test/MOL/MOLtest.jl:17

ERROR: TypeError: non-boolean (Term{Bool, Nothing}) used in boolean context
Stacktrace:

[1] filter(f::DiffEqOperators.var"#182#215"{Num}, a::Vector{Num})

@ Base ./array.jl:2507

[2] symbolic_discretize(pdesys::PDESystem, discretization::MOLFiniteDifference{Vector{Pair{Num, Float64}}, Num})

@ DiffEqOperators ~/Documents/SciML/DiffEqOperators.jl/src/MOLFiniteDifference/MOL_discretization.jl:17

[3] discretize(pdesys::PDESystem, discretization::MOLFiniteDifference{Vector{Pair{Num, Float64}}, Num})

@ DiffEqOperators ~/Documents/SciML/DiffEqOperators.jl/src/MOLFiniteDifference/MOL_discretization.jl:152

[4] top-level scope

@ ~/Documents/SciML/DiffEqOperators.jl/test/MOL/MOLtest.jl:17

The first line that breaks is

nottime = filter(x->x.val != t.val,pdesys.indvars)

The problem is related to this behavior:

julia> typeof(t.val == t.val)
Term{Bool, Nothing}

julia> typeof(t.val === t.val)
Bool

Changing != and == to !== and === everywhere in MOLFiniteDifference removes some of the errors, but there is a "not in" further down

if ModelingToolkit.operation(bc.lhs) isa Sym && t.val ∉ ModelingToolkit.arguments(bc.lhs)

that I don't know how to workaround

[anandijain]

did you try isequal?

[valentinsulzer]

yeah that works, for

t.val ∉ ModelingToolkit.arguments(bc.lhs)

should I replace it with

any(x -> isequal(x.val, t.val), ModelingToolkit.arguments(bc.lhs))

or is there a better way?

[ChrisRackauckas]

I think that's how we have to do it. It was an error to rely on == since that will be interpreted symbolically.

[ChrisRackauckas]

@tinosulzer do you have a WIP PR you're planning to put up here?

[valentinsulzer]

Yes just testing locally now

[ChrisRackauckas]

Thanks!