Serialization & extensions

CTModels keeps heavy, optional dependencies out of its core. Saving solutions (JSON, JLD2) and plotting them live in package extensions under ext/, loaded automatically by Julia only when the trigger package is present.

The public wrappers export_ocp_solution, import_ocp_solution and the plot recipe live in the core; their implementations live in the extension. Until the trigger package is loaded, calling a wrapper raises a descriptive CTBase.ExtensionError — the core never hard- depends on JSON3, JLD2 or Plots.

core wrapper ──(trigger pkg loaded?)──► extension method
     │                  │
export_ocp_solution    no ─► CTBase.ExtensionError
plot recipe            yes ─► JSON3 / JLD2 / Plots implementation

Reading order

A solution to serialize

The examples in this guide reuse one fabricated solution:

using CTModels
using JSON3     # activates the CTModelsJSON extension

pre = CTModels.PreModel()
CTModels.variable!(pre, 0)
CTModels.time!(pre; t0=0.0, tf=1.0)
CTModels.state!(pre, 2)
CTModels.control!(pre, 1)
CTModels.dynamics!(pre, (r, t, x, u, v) -> (r[1] = x[2]; r[2] = u[1]; nothing))
CTModels.objective!(pre, :min; lagrange=(t, x, u, v) -> u[1]^2)
CTModels.time_dependence!(pre; autonomous=true)
ocp = CTModels.build(pre)

N = 101
T = collect(range(0.0, 1.0; length=N))
X = hcat(cos.(T), -sin.(T))
U = reshape(-cos.(T), N, 1)
P = zeros(N, 2)
sol = CTModels.build_solution(ocp, T, X, U, Float64[], P;
    objective=0.5, iterations=10, constraints_violation=1e-9,
    message="ok", status=:optimal, successful=true)

Round-trip in one line each

base = joinpath(tempdir(), "ctmodels_overview")
CTModels.export_ocp_solution(sol; filename=base, format=:JSON)
reloaded = CTModels.import_ocp_solution(ocp; filename=base, format=:JSON)

(CTModels.objective(sol), CTModels.objective(reloaded))

(0.5, 0.5)

See Export & import for the formats and the resampling strategy, and Plotting for the Plots recipe.