Allows for stocks with null upstreams and downstreams (#171)

src/model_parsers/StockFlow.jl

@@ -79,7 +79,7 @@ function parse_askem_model(input::AbstractDict, ::Type{ASKEMStockFlow})
     for param in input[:semantics][:ode][:parameters]
         # want to exclude 
         id = Symbol(param[:id])
-        name = Symbol(param[:name])
+        name = haskey(param,:name) ? Symbol(param[:name]) : :nothing
         value = param[:value]
         expr = only((@parameters $id))
         if haskey(param,:distribution)
@@ -128,6 +128,7 @@ function parse_askem_model(input::AbstractDict, ::Type{ASKEMStockFlow})
         add_part!(d,:Stock, s_name = Symbol(name), s_id = Symbol(id),s_initial = new_initial,s_expr = s_expr)
     end
 
+    add_part!(d,:Stock, s_name = :nothing, s_id = :nothing, s_initial = 0, s_expr = only(@variables null)) #stands in for a source or a sink for now
     # remove the "initial condition" parameters after they've been used
     for initial in input[:semantics][:ode][:initials]
         for i in 1:nparts(d,:Parameter)
@@ -141,7 +142,7 @@ function parse_askem_model(input::AbstractDict, ::Type{ASKEMStockFlow})
         name = Symbol(flow[:name])
         id = Symbol(flow[:id])
         upstream_stock_str = Symbol(flow[:upstream_stock])
-        upstream_stock = only(filter(i -> subpart(d,i,:s_id) == upstream_stock_str, 1:nparts(d,:Stock))) 
+        upstream_stock = only(filter(i -> subpart(d,i,:s_id) == upstream_stock_str, 1:nparts(d,:Stock)))
 
         downstream_stock_str = Symbol(flow[:downstream_stock])
         downstream_stock = only(filter(i -> subpart(d,i,:s_id) == downstream_stock_str, 1:nparts(d,:Stock)))
@@ -169,10 +170,10 @@ function ASKEM_ACSet_to_MTK(sf::ASKEMStockFlow)
     vars_symbolics = [only(@parameters $var) for var in vars_symbols] #ugh the aux_dict line is giving me trouble so I'll do this
     aux_dict = Dict([vars_symbolics[i] => subpart(sf,i,:aux_expr) for i in 1:nparts(sf,:Auxiliary)])
 
-    stock_names = [subpart(sf,n,:s_id) for n in 1:nparts(sf,:Stock)]
+    stock_names = [subpart(sf,n,:s_id) for n in 1:nparts(sf,:Stock) if subpart(sf,n,:s_id) != :nothing]
     stock_funcs = [only(@variables $s(t)) for s in stock_names]
 
-    stock_dict = Dict([subpart(sf,i,:s_expr) => stock_funcs[i] for i in 1:nparts(sf,:Stock)])
+    stock_dict = Dict([subpart(sf,i,:s_expr) => stock_funcs[i] for i in 1:nparts(sf,:Stock) if subpart(sf,i,:s_id) != :nothing])
 
     flow_exprs = [ModelingToolkit.substitute(flow_expr, aux_dict) for flow_expr in aux_flows]
     flow_exprs = [ModelingToolkit.substitute(flow_expr, param_dict) for flow_expr in flow_exprs]
@@ -191,13 +192,13 @@ function ASKEM_ACSet_to_MTK(sf::ASKEMStockFlow)
     inflow_list =  [reduce(+, [flow_exprs[i] for i in inflows(sf,n) if !isempty(inflows(sf,n))], init = 0.0) for n in 1:nparts(sf,:Stock)]
     outflow_list = [reduce(+, [flow_exprs[i] for i in outflows(sf,n) if !isempty(outflows(sf,n))], init = 0.0) for n in 1:nparts(sf,:Stock)]
 
-    eqs = [D(stock_funcs[n]) ~ inflow_list[n] - outflow_list[n] for n in 1:nparts(sf,:Stock)]
+    eqs = [D(stock_funcs[n]) ~ inflow_list[n] - outflow_list[n] for n in 1:nparts(sf,:Stock) if subpart(sf,n,:s_id) != :nothing]
 
     if nparts(sf,:Observable) > 0
         eqs = [eqs ; obs_eqs]
     end
 
-    inits = Dict(stock_funcs .=> [subpart(sf,n,:s_initial) for n in 1:nparts(sf,:Stock)])
+    inits = Dict(stock_funcs .=> [subpart(sf,n,:s_initial) for n in 1:nparts(sf,:Stock) if subpart(sf,n,:s_id) != :nothing])
     paramvals = Dict(paramvars .=> [subpart(sf,n,:p_value) for n in 1:nparts(sf,:Parameter)])
     defaults = merge(inits,paramvals)
     name = subpart(sf,1,:head_name)