merge ss_discrete

Author: vyudu

src/ModelingToolkit.jl

@@ -123,7 +123,6 @@ abstract type AbstractTimeIndependentSystem <: AbstractSystem end
 abstract type AbstractODESystem <: AbstractTimeDependentSystem end
 abstract type AbstractMultivariateSystem <: AbstractSystem end
 abstract type AbstractOptimizationSystem <: AbstractTimeIndependentSystem end
-abstract type AbstractDiscreteSystem <: AbstractTimeDependentSystem end
 
 function independent_variable end
 
@@ -166,7 +165,6 @@ include("systems/diffeqs/modelingtoolkitize.jl")
 include("systems/diffeqs/basic_transformations.jl")
 
 include("systems/discrete_system/discrete_system.jl")
-include("systems/discrete_system/implicit_discrete_system.jl")
 
 include("systems/jumps/jumpsystem.jl")
 
@@ -232,7 +230,6 @@ export DAEFunctionExpr, DAEProblemExpr
 export SDESystem, SDEFunction, SDEFunctionExpr, SDEProblemExpr
 export SystemStructure
 export DiscreteSystem, DiscreteProblem, DiscreteFunction, DiscreteFunctionExpr
-export ImplicitDiscreteSystem, ImplicitDiscreteProblem, ImplicitDiscreteFunction, ImplicitDiscreteFunctionExpr
 export JumpSystem
 export ODEProblem, SDEProblem
 export NonlinearFunction, NonlinearFunctionExpr

src/structural_transformation/StructuralTransformations.jl

@@ -22,7 +22,7 @@ using ModelingToolkit: ODESystem, AbstractSystem, var_from_nested_derivative, Di
                        get_postprocess_fbody, vars!,
                        IncrementalCycleTracker, add_edge_checked!, topological_sort,
                        invalidate_cache!, Substitutions, get_or_construct_tearing_state,
-                       filter_kwargs, lower_varname_with_unit, setio, SparseMatrixCLIL,
+                       filter_kwargs, lower_varname_with_unit, lower_shift_varname_with_unit, setio, SparseMatrixCLIL,
                        get_fullvars, has_equations, observed,
                        Schedule, schedule
 
@@ -63,6 +63,7 @@ export torn_system_jacobian_sparsity
 export full_equations
 export but_ordered_incidence, lowest_order_variable_mask, highest_order_variable_mask
 export computed_highest_diff_variables
+export shift2term, lower_shift_varname
 
 include("utils.jl")
 include("pantelides.jl")