feat: support inplace parameter observed

src/systems/abstractsystem.jl

@@ -481,7 +481,7 @@ function SymbolicIndexingInterface.is_timeseries_parameter(sys::AbstractSystem,
 end
 
 function SymbolicIndexingInterface.timeseries_parameter_index(sys::AbstractSystem, sym)
-    has_index_cache(sys) && (ic = get_index_cache(sys)) !== nothing || return false
+    has_index_cache(sys) && (ic = get_index_cache(sys)) !== nothing || return nothing
     timeseries_parameter_index(ic, sym)
 end
 
@@ -504,9 +504,17 @@ function SymbolicIndexingInterface.parameter_observed(sys::AbstractSystem, sym)
         else
             ts_idx = nothing
         end
-        obsfn = let raw_obs_fn = build_explicit_observed_function(
-                sys, sym; param_only = true)
-            f(p::MTKParameters, t) = raw_obs_fn(p..., t)
+        rawobs = build_explicit_observed_function(
+                sys, sym; param_only = true, return_inplace = true)
+        if rawobs isa Tuple
+            obsfn = let oop = rawobs[1], iip = rawobs[2]
+                f1(p::MTKParameters, t) = oop(p..., t)
+                f1(out, p::MTKParameters, t) = iip(out, p..., t)
+            end
+        else
+            obsfn = let rawobs = rawobs
+                f2(p::MTKParameters, t) = rawobs(p..., t)
+            end
         end
     else
         ts_idx = nothing

src/systems/diffeqs/odesystem.jl

@@ -381,6 +381,7 @@ function build_explicit_observed_function(sys, ts;
         drop_expr = drop_expr,
         ps = full_parameters(sys),
         param_only = false,
+        return_inplace = false,
         op = Operator,
         throw = true)
     if (isscalar = symbolic_type(ts) !== NotSymbolic())
@@ -490,7 +491,13 @@ function build_explicit_observed_function(sys, ts;
         args = param_only ? [ipts, ps..., ivs...] : [dvs, ipts, ps..., ivs...]
     end
     pre = get_postprocess_fbody(sys)
-
+    res = build_function(isscalar ? ts[1] : ts, args...; get_postprocess_fbody = pre, wrap_code = wrap_array_vars(sys, isscalar ? ts[1] : ts; dvs = param_only ? [] : unknowns(sys)), expression = Val{expression})
+    if isscalar || return_inplace
+        return res
+    else
+        return res[1]
+    end
+
     ex = Func(args, [],
              pre(Let(obsexprs,
                  isscalar ? ts[1] : MakeArray(ts, output_type),

src/systems/index_cache.jl

@@ -127,7 +127,6 @@ function IndexCache(sys::AbstractSystem)
                 if istree(sym) && operation(sym) == Shift(t, 1)
                     sym = only(arguments(sym))
                 end
-                # is_parameter(sys, sym) || is_parameter(sys, Hold(sym)) || continue
                 disc_clocks[sym] = i - 1
                 disc_clocks[sym] = i - 1
                 disc_clocks[default_toterm(sym)] = i - 1