Add simple resistor example

MechatronicsModeling.jl/Project.toml

@@ -0,0 +1,4 @@
+[deps]
+GLMakie = "e9467ef8-e4e7-5192-8a1a-b1aee30e663a"
+ModelingToolkit = "961ee093-0014-501f-94e3-6117800e7a78"
+OrdinaryDiffEq = "1dea7af3-3e70-54e6-95c3-0bf5283fa5ed"

MechatronicsModeling.jl/r_circuit.jl

@@ -0,0 +1,41 @@
+using ModelingToolkit, OrdinaryDiffEq
+using GLMakie
+
+@parameters R
+@variables t v(t) i(t)
+D = Differential(t)
+
+eqs = [
+   i ~ v/R
+   D(v) ~ 0
+]
+
+@named circuit = ODESystem(eqs, t)
+
+function solve_circuit(circuit)
+    u0 = [
+       v => 5.0,
+    ]
+
+    p = [
+       R => 10,
+    ]
+
+    tspan = (0.0, 0.01)
+    # convert the DAE problem to an ODE problem
+    circuit = structural_simplify(circuit)
+    prob = ODEProblem(circuit, u0, tspan, p)
+    sol = solve(prob, Tsit5())
+
+    # Interpolation can give the solution inside tspan and also further
+    #sol(0.009)
+    return sol
+end
+
+
+function show_sol(circuit)
+    sol = solve_circuit(circuit)
+    lines(sol.t, sol[i], color = :red)
+    lines!(sol.t, sol[v], color = :blue)
+    current_figure()
+end