docs: use @mtkbuild in place of redundant structural_simplify

Author: AayushSabharwal

docs/src/basics/Events.md

@@ -93,11 +93,9 @@ D = Differential(t)
 root_eqs = [x ~ 0]  # the event happens at the ground x(t) = 0
 affect = [v ~ -v] # the effect is that the velocity changes sign
 
-@named ball = ODESystem([D(x) ~ v
+@mtkbuild ball = ODESystem([D(x) ~ v
         D(v) ~ -9.8], t; continuous_events = root_eqs => affect) # equation => affect
 
-ball = structural_simplify(ball)
-
 tspan = (0.0, 5.0)
 prob = ODEProblem(ball, Pair[], tspan)
 sol = solve(prob, Tsit5())
@@ -116,15 +114,13 @@ D = Differential(t)
 continuous_events = [[x ~ 0] => [vx ~ -vx]
     [y ~ -1.5, y ~ 1.5] => [vy ~ -vy]]
 
-@named ball = ODESystem([
+@mtkbuild ball = ODESystem([
         D(x) ~ vx,
         D(y) ~ vy,
         D(vx) ~ -9.8 - 0.1vx, # gravity + some small air resistance
         D(vy) ~ -0.1vy,
     ], t; continuous_events)
 
-ball = structural_simplify(ball)
-
 tspan = (0.0, 10.0)
 prob = ODEProblem(ball, Pair[], tspan)
 
@@ -197,10 +193,9 @@ end
 
 reflect = [x ~ 0] => (bb_affect!, [v], [], nothing)
 
-@named bb_model = ODESystem(bb_eqs, t, sts, par,
+@mtkbuild bb_sys = ODESystem(bb_eqs, t, sts, par,
     continuous_events = reflect)
 
-bb_sys = structural_simplify(bb_model)
 u0 = [v => 0.0, x => 1.0]
 
 bb_prob = ODEProblem(bb_sys, u0, (0, 5.0))

docs/src/basics/FAQ.md

@@ -141,7 +141,6 @@ using ModelingToolkit, StaticArrays
 sts = @variables x1(t)=0.0
 D = Differential(t)
 eqs = [D(x1) ~ 1.1 * x1]
-@named sys = ODESystem(eqs, t)
-sys = structural_simplify(sys)
+@mtkbuild sys = ODESystem(eqs, t)
 prob = ODEProblem{false}(sys, [], (0,1); u0_constructor = x->SVector(x...))
 ```

docs/src/examples/perturbation.md

@@ -92,8 +92,7 @@ We are nearly there! From this point on, the rest is standard ODE solving proced
 ```julia
 using ModelingToolkit, DifferentialEquations
 
-@named sys = ODESystem(eqs, t)
-sys = structural_simplify(sys)
+@mtkbuild sys = ODESystem(eqs, t)
 unknowns(sys)
 ```
 
@@ -158,8 +157,7 @@ eqs = [substitute(first(v), subs) ~ substitute(last(v), subs) for v in vals]
 We continue with converting 'eqs' to an `ODEProblem`, solving it, and finally plot the results against the exact solution to the original problem, which is $x(t, \epsilon) = (1 - \epsilon)^{-1/2} e^{-\epsilon t} \sin((1- \epsilon^2)^{1/2}t)$,
 
 ```julia
-@named sys = ODESystem(eqs, t)
-sys = structural_simplify(sys)
+@mtkbuild sys = ODESystem(eqs, t)
 ```
 
 ```julia