fix: fix array discrete parameters

[AayushSabharwal]

Close #3990

[sablonl]

The fix works well when the parameter is a vector, but I still get an error with solve when it's a matrix:

MRE:

using Pkg;
Pkg.activate(temp = true)

Pkg.add(url="https://github.com/AayushSabharwal/ModelingToolkit.jl", rev="as/event-bugs")
Pkg.add("OrdinaryDiffEqTsit5")

using ModelingToolkit
using ModelingToolkit: t_nounits as t, D_nounits as D
using OrdinaryDiffEqTsit5

N = 2
@parameters s(t)::Float64
@parameters v(t)[1:N]::Float64
@parameters M(t)[1:N, 1:N]::Float64

@variables x(t)::Float64

Mini = rand(N, N) ./ (N^2)
vini = vec(sum(Mini, dims = 1))
sMini = sum(Mini)

s_eq = [D(x) ~ x * s]
v_eq = [D(x) ~ x * Symbolics.scalarize(sum(v))]
M_eq = [D(x) ~ x * Symbolics.scalarize(sum(M))]


s_event = ModelingToolkit.SymbolicDiscreteCallback(
	1.0,
	[s ~ -Pre(s)],
	discrete_parameters = [s],
)

v_event = ModelingToolkit.SymbolicDiscreteCallback(
	1.0,
	[v ~ -Pre(v)],
	discrete_parameters = [v], # replacing with collect(v) works
)

M_event = ModelingToolkit.SymbolicDiscreteCallback(
	1.0,
	[M ~ -Pre(M)],
	discrete_parameters = [M], # replacing with collect(M) still errors
)

@mtkcompile s_sys = System(s_eq, t; discrete_events = s_event)
@mtkcompile v_sys = System(v_eq, t; discrete_events = v_event)
@mtkcompile M_sys = System(M_eq, t; discrete_events = M_event)

u0p0_map = Dict(x => 1.0, M => Mini, s => sMini, v => vini)

s_prob = ODEProblem(s_sys, u0p0_map, (0.0, 2.5))
v_prob = ODEProblem(v_sys, u0p0_map, (0.0, 2.5))
M_prob = ODEProblem(M_sys, u0p0_map, (0.0, 2.5))

s_sol = solve(s_prob, Tsit5()) #, tstops = 1.0) # perfect
v_sol = solve(v_prob, Tsit5()) #, tstops = 1.0) # perfect
M_sol = solve(M_prob, Tsit5()) #, tstops = 1.0) # fails
perfect

# using Plots
# plot(s_sol, label = "s event")
# plot!(v_sol, label = "v event")
# plot!(M_sol, label = "M event")

with

julia> show(err)
1-element ExceptionStack:
LoadError: MethodError: Cannot `convert` an object of type 
  ModelingToolkit.NestedGetIndex{Tuple{Array{Matrix{Float64},1}}} to an object of type 
  ModelingToolkit.NestedGetIndex{Tuple{Array{Base.ReshapedArray{Float64, 2, SubArray{Float64, 1, Vector{Float64}, Tuple{UnitRange{Int64}}, true}, Tuple{}},1}}}
The function `convert` exists, but no method is defined for this combination of argument types.

Closest candidates are:
  (::Type{ModelingToolkit.NestedGetIndex{T}} where T)(::Any)
   @ ModelingToolkit /cyfast/lsablon/.julia/packages/ModelingToolkit/75pJw/src/systems/parameter_buffer.jl:801
  convert(::Type{T}, ::T) where T
   @ Base Base_compiler.jl:133

[AayushSabharwal]

Amazing, thanks for trying it out and for the MWE. I'll patch it.

[AayushSabharwal]

InterfaceII is fixed in another PR