identity f to DiscreteFunction

Author: isaacsas

src/problem.jl

@@ -12,7 +12,7 @@ end
 
 ### DiscreteProblem, passing through syms
 function DiffEqBase.DiscreteProblem(rn::DiffEqBase.AbstractReactionNetwork, u0, tspan::Tuple, p=nothing; kwargs...)
-    f = DiffEqBase.DISCRETE_INPLACE_DEFAULT
+    f = (du,u,p,t) -> du.=u    # identity function to make syms works
     df = DiscreteFunction(f,syms=rn.syms)
     DiscreteProblem(df, u0, tspan, p; kwargs...)
 end