feat: implement isapprox for systems

Author: AayushSabharwal

src/systems/system.jl

@@ -1097,3 +1097,51 @@ function supports_initialization(sys::System)
     return isempty(jumps(sys)) && _iszero(cost(sys)) &&
            isempty(constraints(sys))
 end
+
+safe_eachrow(::Nothing) = nothing
+safe_eachrow(x::AbstractArray) = eachrow(x)
+
+safe_issetequal(::Nothing, ::Nothing) = true
+safe_issetequal(::Nothing, x) = false
+safe_issetequal(x, ::Nothing) = false
+safe_issetequal(x, y) = issetequal(x, y)
+
+"""
+    $(TYPEDSIGNATURES)
+
+Check if two systems are about equal, to the extent that ModelingToolkit.jl supports. Note
+that if this returns `true`, the systems are not guaranteed to be exactly equivalent
+(unless `sysa === sysb`) but are highly likely to represent a similar mathematical problem.
+If this returns `false`, the systems are very likely to be different.
+"""
+function Base.isapprox(sysa::System, sysb::System)
+    sysa === sysb && return true
+    return nameof(sysa) == nameof(sysb) &&
+           isequal(get_iv(sysa), get_iv(sysb)) &&
+           issetequal(get_eqs(sysa), get_eqs(sysb)) &&
+           issetequal(safe_eachrow(get_noise_eqs(sysa)), safe_eachrow(get_noise_eqs(sysb))) &&
+           issetequal(get_jumps(sysa), get_jumps(sysb)) &&
+           issetequal(get_constraints(sysa), get_constraints(sysb)) &&
+           issetequal(get_costs(sysa), get_costs(sysb)) &&
+           isequal(get_consolidate(sysa), get_consolidate(sysb)) &&
+           issetequal(get_unknowns(sysa), get_unknowns(sysb)) &&
+           issetequal(get_ps(sysa), get_ps(sysb)) &&
+           issetequal(get_brownians(sysa), get_brownians(sysb)) &&
+           issetequal(get_observed(sysa), get_observed(sysb)) &&
+           issetequal(get_parameter_dependencies(sysa), get_parameter_dependencies(sysb)) &&
+           isequal(get_description(sysa), get_description(sysb)) &&
+           isequal(get_defaults(sysa), get_defaults(sysb)) &&
+           isequal(get_guesses(sysa), get_guesses(sysb)) &&
+           issetequal(get_initialization_eqs(sysa), get_initialization_eqs(sysb)) &&
+           issetequal(get_continuous_events(sysa), get_continuous_events(sysb)) &&
+           issetequal(get_discrete_events(sysa), get_discrete_events(sysb)) &&
+           isequal(get_connector_type(sysa), get_connector_type(sysb)) &&
+           isequal(get_assertions(sysa), get_assertions(sysb)) &&
+           isequal(get_metadata(sysa), get_metadata(sysb)) &&
+           isequal(get_is_dde(sysa), get_is_dde(sysb)) &&
+           issetequal(get_tstops(sysa), get_tstops(sysb)) &&
+           safe_issetequal(get_ignored_connections(sysa), get_ignored_connections(sysb)) &&
+           isequal(get_is_initializesystem(sysa), get_is_initializesystem(sysb)) &&
+           isequal(get_is_discrete(sysa), get_is_discrete(sysb)) &&
+           isequal(get_isscheduled(sysa), get_isscheduled(sysb))
+end

test/serialization.jl

@@ -28,6 +28,7 @@ str = String(take!(io))
 
 sys = include_string(@__MODULE__, str)
 rc2 = expand_connections(rc_model)
+@test isapprox(sys, rc2)
 @test issetequal(equations(sys), equations(rc2))
 @test issetequal(unknowns(sys), unknowns(rc2))
 @test issetequal(parameters(sys), parameters(rc2))