Make tests pass

Author: sharanry

src/systems/discrete_system/discrete_system.jl

@@ -186,7 +186,8 @@ function generate_function(
     eqs = equations(sys)
     foreach(check_difference_variables, eqs)
     # substitute x(t) by just x
-    rhss = [isdifference(eq.lhs) ? arguments(eq.lhs)[1] + eq.rhs : eq.rhs for eq in eqs]
+    # rhss = [isdifference(eq.lhs) ? arguments(eq.lhs)[1] + eq.rhs : eq.rhs for eq in eqs]
+    rhss = [eq.rhs for eq in eqs]
 
     u = map(x->time_varying_as_func(value(x), sys), dvs)
     p = map(x->time_varying_as_func(value(x), sys), ps)

test/discretesystem.jl

@@ -11,15 +11,16 @@ end;
 
 # Independent and dependent variables and parameters
 @parameters t c nsteps δt β γ
+D = Difference(t; dt=0.1)
 @variables S(t) I(t) R(t) next_S(t) next_I(t) next_R(t)
 
 infection = rate_to_proportion(β*c*I/(S+I+R),δt)*S
 recovery = rate_to_proportion(γ,δt)*I
 
 # Equations
-eqs = [next_S ~ S-infection,
-       next_I ~ I+infection-recovery,
-       next_R ~ R+recovery]
+eqs = [D(S) ~ S-infection,
+       D(I) ~ I+infection-recovery,
+       D(R) ~ R+recovery]
 
 # System
 sys = DiscreteSystem(eqs,t,[S,I,R],[c,nsteps,δt,β,γ]; controls = [β, γ])
@@ -36,16 +37,16 @@ sol_map = solve(prob_map,FunctionMap());
 
 # Direct Implementation
 
-function sir_map!(u_new,u,p,t)
+function sir_map!(u_diff,u,p,t)
     (S,I,R) = u
     (β,c,γ,δt) = p
     N = S+I+R
     infection = rate_to_proportion(β*c*I/N,δt)*S
     recovery = rate_to_proportion(γ,δt)*I
     @inbounds begin
-        u_new[1] = S-infection
-        u_new[2] = I+infection-recovery
-        u_new[3] = R+recovery
+        u_diff[1] = S-infection
+        u_diff[2] = I+infection-recovery
+        u_diff[3] = R+recovery
     end
     nothing
 end;