Plotting does not work if system does not have dynamics

[asinghvi17]

Describe the bug 🐞

I have a sine oscillator with only observed quantities, no dynamics or differential equations. Plotting doesn't work here.

Expected behavior

Something should be plotted.

Minimal Reproducible Example 👇

MWE is in comment number 2 (note it's BSD-3 code so fine to distribute)

Error & Stacktrace ⚠️

julia> lines(sol)
ERROR: BoundsError: attempt to access 0-element Vector{Tuple} at index [1]
Stacktrace:
  [1] throw_boundserror(A::Vector{Tuple}, I::Tuple{Int64})
    @ Base ./essentials.jl:14
  [2] getindex
    @ ./essentials.jl:916 [inlined]
  [3] diffeq_to_arrays(sol::SciMLBase.ODESolution{…}, plot_analytic::Bool, denseplot::Bool, plotdensity::Int64, tspan::Nothing, vars::Vector{…}, tscale::Symbol, plotat::Nothing)
    @ SciMLBase ~/.julia/packages/SciMLBase/Ha7rZ/src/solutions/solution_interface.jl:453
  [4] convert_arguments(PT::Type{…}, sol::SciMLBase.ODESolution{…}; plot_analytic::Bool, denseplot::MakieCore.Automatic, plotdensity::MakieCore.Automatic, plotat::Nothing, tspan::Nothing, tscale::Symbol, vars::Nothing, idxs::Nothing)
    @ SciMLBaseMakieExt ~/.julia/packages/SciMLBase/Ha7rZ/ext/SciMLBaseMakieExt.jl:108
  [5] convert_arguments(PT::Type{…}, sol::SciMLBase.ODESolution{…})
    @ SciMLBaseMakieExt ~/.julia/packages/SciMLBase/Ha7rZ/ext/SciMLBaseMakieExt.jl:38

Environment (please complete the following information):
MTK v9 but otherwise irrelevant

[ChrisRackauckas]

It does though, I had just fixed it up like 3 weeks ago and there's a test on it. I. That case you have two saves so you will have a line, so please give an mwe

[asinghvi17]

@component function Sine(; name, start_time=0, offset=0, amplitude=nothing, frequency=nothing, phase=0)

  ### Symbolic Parameters
  __params = Any[]
  append!(__params, @parameters (start_time::Float64 = start_time))
  append!(__params, @parameters (offset::Float64 = offset))
  append!(__params, @parameters (amplitude::Float64 = amplitude))
  append!(__params, @parameters (frequency::Float64 = frequency))
  append!(__params, @parameters (phase::Float64 = phase))

  ### Variables
  __vars = Any[]
  append!(__vars, @variables y(t), [output = true])

  ### Constants
  __constants = Any[]

  ### Components
  __systems = ODESystem[]

  ### Defaults
  __defaults = Dict()

  ### Initialization Equations
  __initialization_eqs = []

  ### Equations
  __eqs = Equation[]
  push!(__eqs, y ~ ifelse(start_time < t, offset + amplitude * sin(2 * π * frequency * (t - start_time) + phase), offset))

  # Return completely constructed ODESystem
  return ODESystem(__eqs, t, __vars, __params; systems=__systems, defaults=__defaults, name, initialization_eqs=__initialization_eqs)
end

then

@mtkbuild model = Sine()
prob = ODEProblem(model, [], (0, 10))
sol = solve(model)

plotting this sol is what fails:

plot(sol)

[oscardssmith]

it's possible this is a version issue... What's ]st?

[asinghvi17]

⌅ [961ee093] ModelingToolkit v9.79.1
[1dea7af3] OrdinaryDiffEq v6.98.0
[0bca4576] SciMLBase v2.96.0

[ChrisRackauckas]

The MWE was fine:

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

@component function Sine(; name, start_time=0, offset=0, amplitude=nothing, frequency=nothing, phase=0)

  ### Symbolic Parameters
  __params = Any[]
  append!(__params, @parameters (start_time::Float64 = start_time))
  append!(__params, @parameters (offset::Float64 = offset))
  append!(__params, @parameters (amplitude::Float64 = amplitude))
  append!(__params, @parameters (frequency::Float64 = frequency))
  append!(__params, @parameters (phase::Float64 = phase))

  ### Variables
  __vars = Any[]
  append!(__vars, @variables y(t), [output = true])

  ### Constants
  __constants = Any[]

  ### Components
  __systems = ODESystem[]

  ### Defaults
  __defaults = Dict()

  ### Initialization Equations
  __initialization_eqs = []

  ### Equations
  __eqs = Equation[]
  push!(__eqs, y ~ ifelse(start_time < t, offset + amplitude * sin(2 * π * frequency * (t - start_time) + phase), offset))

  # Return completely constructed ODESystem
  return ODESystem(__eqs, t, __vars, __params; systems=__systems, defaults=__defaults, name, initialization_eqs=__initialization_eqs)
end

@mtkbuild model = Sine(amplitude=1.0, frequency=1.0)
prob = ODEProblem(model, [], (0, 10))
sol = solve(prob)

using Plots
plot(sol)
plot(sol; idxs=model.y)

I had to fix it: it was clear you didn't run your MWE.

[asinghvi17]

Huh. I guess the error only happens in Makie, for which I can replicate:

import CairoMakie
CairoMakie.plot(sol)

So there's clearly some divergence between those. I'll look at that and try to clean this up.

[asinghvi17]

Ah yep, there's quite a bit of difference there.

[asinghvi17]

SciMLBase.jl/src/solutions/solution_interface.jl

Lines 368 to 371 in 28cb4df

	# Scatterplot of points
	@series begin
	seriestype := :line
	linestyle --> :dash

This says it's a scatter plot but the series type is a line - which do we want here?

[ChrisRackauckas]

It's not a scatter plot. And you forgot the idxs, CairoMakie.plot(sol; idxs = model.y)