Merge pull request #1188 from SciML/sm/hist

Add the `hist` function

Author: YingboMa

src/systems/abstractsystem.jl

@@ -945,12 +945,14 @@ by default.
 function extend(sys::AbstractSystem, basesys::AbstractSystem; name::Symbol=nameof(sys))
     T = SciMLBase.parameterless_type(basesys)
     ivs = independent_variables(basesys)
-    if length(ivs) == 0
-        sys = convert_system(T, sys)
-    elseif length(ivs) == 1
-        sys = convert_system(T, sys, ivs[1])
-    else
-        throw("Extending multivariate systems is not supported")
+    if !(typeof(sys) <: T)
+        if length(ivs) == 0
+            sys = convert_system(T, sys)
+        elseif length(ivs) == 1
+            sys = convert_system(T, sys, ivs[1])
+        else
+            throw("Extending multivariate systems is not supported")
+        end
     end
 
     eqs = union(equations(basesys), equations(sys))

src/utils.jl

@@ -108,7 +108,7 @@ end
 function check_variables(dvs, iv)
     for dv in dvs
         isequal(iv, dv) && throw(ArgumentError("Independent variable $iv not allowed in dependent variables."))
-        isequal(iv, iv_from_nested_derivative(dv)) || throw(ArgumentError("Variable $dv is not a function of independent variable $iv."))
+        occursin(iv, iv_from_nested_derivative(dv)) || throw(ArgumentError("Variable $dv is not a function of independent variable $iv."))
     end
 end
 

src/variables.jl

@@ -75,3 +75,9 @@ function _varmap_to_vars(varmap::Dict, varlist; defaults=Dict(), check=false, to
 end
 
 @noinline throw_missingvars(vars) = throw(ArgumentError("$vars are missing from the variable map."))
+
+struct IsHistory end
+ishistory(x) = ishistory(unwrap(x))
+ishistory(x::Symbolic) = getmetadata(x, IsHistory, false)
+hist(x, t) = wrap(hist(unwrap(x), t))
+hist(x::Symbolic, t) = setmetadata(toparam(similarterm(x, operation(x), [unwrap(t)], metadata=metadata(x))), IsHistory, true)

test/odesystem.jl

@@ -458,3 +458,12 @@ end
 
 @variables t
 @named sys = ODESystem([0 ~ sys1.y + sys2.y ], t; systems=[sys1, sys2])
+
+# DelayDiffEq
+using ModelingToolkit: hist
+@variables t x(t) y(t)
+D = Differential(t)
+xₜ₋₁ = hist(x, t-1)
+eqs = [D(x) ~ x * y
+       D(y) ~ y * x - xₜ₋₁]
+@named sys = ODESystem(eqs, t)