refactor: remove all references to isdifferenceeq and DiscreteSystem

Author: AayushSabharwal

docs/pages.jl

@@ -32,7 +32,6 @@ pages = [
         "systems/JumpSystem.md",
         "systems/NonlinearSystem.md",
         "systems/OptimizationSystem.md",
-        "systems/DiscreteSystem.md",
         "systems/PDESystem.md"],
     "comparison.md",
     "internals.md",

docs/src/systems/DiscreteSystem.md

@@ -24,7 +24,7 @@ structural_simplify
 ## Problem Constructors
 
 ```@docs; canonical=false
-DiscreteProblem(sys::ModelingToolkit.DiscreteSystem, u0map, tspan)
+DiscreteProblem(sys::JumpSystem, u0map, tspan)
 ```
 
 ```@docs

docs/src/systems/JumpSystem.md

@@ -215,7 +215,7 @@ function generate_control_function(sys::AbstractODESystem, inputs = unbound_inpu
     end
     inputs = map(x -> time_varying_as_func(value(x), sys), inputs)
 
-    eqs = [eq for eq in full_equations(sys) if !isdifferenceeq(eq)]
+    eqs = [eq for eq in full_equations(sys)]
     if disturbance_inputs !== nothing
         # Set all disturbance *inputs* to zero (we just want to keep the disturbance state)
         subs = Dict(disturbance_inputs .=> 0)

src/inputoutput.jl

@@ -1,6 +1,6 @@
 using LinearAlgebra
 
-using ModelingToolkit: isdifferenceeq, process_events, get_preprocess_constants
+using ModelingToolkit: process_events, get_preprocess_constants
 
 const MAX_INLINE_NLSOLVE_SIZE = 8
 

src/structural_transformation/codegen.jl

@@ -148,7 +148,7 @@ function generate_function(sys::AbstractODESystem, dvs = unknowns(sys), ps = par
     if isdde
         eqs = delay_to_function(sys)
     else
-        eqs = [eq for eq in equations(sys) if !isdifferenceeq(eq)]
+        eqs = [eq for eq in equations(sys)]
     end
     if !implicit_dae
         check_operator_variables(eqs, Differential)
@@ -225,7 +225,7 @@ function delay_to_function(expr, iv, sts, ps, h)
 end
 
 function calculate_massmatrix(sys::AbstractODESystem; simplify = false)
-    eqs = [eq for eq in equations(sys) if !isdifferenceeq(eq)]
+    eqs = [eq for eq in equations(sys)]
     dvs = unknowns(sys)
     M = zeros(length(eqs), length(eqs))
     unknown2idx = Dict(s => i for (i, s) in enumerate(dvs))
@@ -891,9 +891,6 @@ function DiffEqBase.ODEProblem{iip, specialize}(sys::AbstractODESystem, u0map =
         callback = nothing,
         check_length = true,
         kwargs...) where {iip, specialize}
-    has_difference = any(isdifferenceeq, equations(sys))
-    has_difference &&
-        error("The operators Difference and DiscreteUpdate are deprecated. Use ShiftIndex instead.")
     f, u0, p = process_DEProblem(ODEFunction{iip, specialize}, sys, u0map, parammap;
         t = tspan !== nothing ? tspan[1] : tspan,
         check_length, kwargs...)
@@ -962,9 +959,6 @@ end
 function DiffEqBase.DAEProblem{iip}(sys::AbstractODESystem, du0map, u0map, tspan,
         parammap = DiffEqBase.NullParameters();
         check_length = true, kwargs...) where {iip}
-    has_difference = any(isdifferenceeq, equations(sys))
-    has_difference &&
-        error("The operators Difference and DiscreteUpdate are deprecated. Use ShiftIndex instead.")
     f, du0, u0, p = process_DEProblem(DAEFunction{iip}, sys, u0map, parammap;
         implicit_dae = true, du0map = du0map, check_length,
         kwargs...)
@@ -990,9 +984,6 @@ function DiffEqBase.DDEProblem{iip}(sys::AbstractODESystem, u0map = [],
         callback = nothing,
         check_length = true,
         kwargs...) where {iip}
-    has_difference = any(isdifferenceeq, equations(sys))
-    has_difference &&
-        error("The operators Difference and DiscreteUpdate are deprecated. Use ShiftIndex instead.")
     f, u0, p = process_DEProblem(DDEFunction{iip}, sys, u0map, parammap;
         t = tspan !== nothing ? tspan[1] : tspan,
         symbolic_u0 = true,
@@ -1051,9 +1042,6 @@ function DiffEqBase.SDDEProblem{iip}(sys::AbstractODESystem, u0map = [],
         check_length = true,
         sparsenoise = nothing,
         kwargs...) where {iip}
-    has_difference = any(isdifferenceeq, equations(sys))
-    has_difference &&
-        error("The operators Difference and DiscreteUpdate are deprecated. Use ShiftIndex instead.")
     f, u0, p = process_DEProblem(SDDEFunction{iip}, sys, u0map, parammap;
         t = tspan !== nothing ? tspan[1] : tspan,
         symbolic_u0 = true,

src/systems/diffeqs/abstractodesystem.jl

@@ -36,7 +36,6 @@ end
 function __structural_simplify(sys::AbstractSystem, io = nothing; simplify = false,
         kwargs...)
     sys = expand_connections(sys)
-    sys isa DiscreteSystem && return sys
     state = TearingState(sys)
 
     @unpack structure, fullvars = state