Ensure that generate_ode_function always returns Expr

Author: YingboMa

src/systems/diffeqs/diffeqsystem.jl

@@ -43,7 +43,7 @@ function generate_ode_function(sys::DiffEqSystem)
     dvar_exprs = [:(du[$i] = $(Symbol("$(sys.dvs[i].name)_$(sys.ivs[1].name)"))) for i in 1:length(sys.dvs)]
     exprs = vcat(var_exprs,param_exprs,sys_exprs,dvar_exprs)
     block = expr_arr_to_block(exprs)
-    :((du,u,p,t)->$(block))
+    :((du,u,p,t)->$(toexpr(block)))
 end
 
 isintermediate(eq) = eq.args[1].diff == nothing

src/utils.jl

@@ -1,3 +1,4 @@
+using MacroTools
 function expr_arr_to_block(exprs)
   block = :(begin end)
   foreach(expr -> push!(block.args, expr), exprs)
@@ -15,3 +16,5 @@ function flatten_expr!(x)
     end
     x
 end
+
+toexpr(ex) = MacroTools.postwalk(x->x isa Union{Expression,Operation} ? Expr(x) : x, ex)

test/system_construction.jl

@@ -82,6 +82,15 @@ end
 
 ModelingToolkit.generate_nlsys_function(ns)
 
+@Var _x
+@Deriv D'~t
+@Param A B C
+eqs = [_x ~ y/C,
+       D*x ~ -A*x,
+       D*y ~ A*x - B*_x]
+de = DiffEqSystem(eqs,[t],[x,y],Variable[_x],[A,B,C])
+@test eval(ModelingToolkit.generate_ode_function(de))([0.0,0.0],[1.0,2.0],[1,2,3],0.0) ≈ -1/3
+
 # Now nonlinear system with only variables
 @Var x y z
 @Param σ ρ β