From 303962d5b983891074165786f34d4522b457c8d5 Mon Sep 17 00:00:00 2001
From: Luke Morris <lukelukemorrismorris@gmail.com>
Date: Sun, 25 Aug 2024 19:40:08 -0400
Subject: [PATCH] Compute longest paths from terminals

---
 src/DiagrammaticEquations.jl | 2 +-
 src/graph_traversal.jl       | 7 ++++---
 test/graph_traversal.jl      | 6 ++++++
 3 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/src/DiagrammaticEquations.jl b/src/DiagrammaticEquations.jl
index 5ab376a..978428c 100644
--- a/src/DiagrammaticEquations.jl
+++ b/src/DiagrammaticEquations.jl
@@ -5,7 +5,7 @@ module DiagrammaticEquations
 using Catlab
 
 export
-DerivOp, append_dot, normalize_unicode, infer_states, infer_types!,
+DerivOp, append_dot, normalize_unicode, infer_states, infer_terminals, infer_types!,
 # Deca
 op1_res_rules_1D, op2_res_rules_1D, op1_res_rules_2D, op2_res_rules_2D,
 op1_inf_rules_1D, op2_inf_rules_1D, op1_inf_rules_2D, op2_inf_rules_2D,
diff --git a/src/graph_traversal.jl b/src/graph_traversal.jl
index 5e8c794..4e61538 100644
--- a/src/graph_traversal.jl
+++ b/src/graph_traversal.jl
@@ -29,7 +29,6 @@ number_of_ops(d::SummationDecapode) = nparts(d, :Op1) + nparts(d, :Op2) + nparts
 
 start_nodes(d::SummationDecapode) = vcat(infer_states(d), incident(d, :Literal, :type))
 
-
 # TODO: This could be Catlab'd. Hypergraph category? Migration to a DWD?
 """    function hyper_edge_list(d::SummationDecapode)
 
@@ -55,11 +54,13 @@ Taking the maximum of the non-infinite short paths from state variables induces
 https://en.wikipedia.org/wiki/Floyd–Warshall_algorithm
 """
 function floyd_warshall(d::SummationDecapode)
+  # Define weights.
+  w(e) = (length(e.dom) == 1 && e.name ∈ [:∂ₜ,:dt]) ? -Inf : -1
   # Init dists
   V = nparts(d, :Var)
   dist = fill(Inf, (V, V))
   foreach(hyper_edge_list(d)) do e
-    dist[(e.dom), e.cod] .= 1
+    dist[(e.dom), e.cod] .= w(e)
   end
   for v in 1:V
     dist[v,v] = 0
@@ -86,7 +87,7 @@ The vector returned by this function maps each vertex to the order that it would
 function topological_sort_verts(d::SummationDecapode)
   m = floyd_warshall(d)
   map(parts(d,:Var)) do v
-    maximum(filter(!isinf, m[start_nodes(d),v]))
+    minimum(filter(!isinf, m[v,infer_terminals(d)]))
   end
 end
 
diff --git a/test/graph_traversal.jl b/test/graph_traversal.jl
index 825de65..9160b05 100644
--- a/test/graph_traversal.jl
+++ b/test/graph_traversal.jl
@@ -64,4 +64,10 @@ end
   end
   result = topological_sort_edges(op_combo)
   @test is_correct_length(op_combo, result)
+
+  sum_with_single_dependency = @decapode begin
+    F == A + f(A) + h(g(A))
+  end
+  result = topological_sort_edges(sum_with_single_dependency)
+  @test is_correct_length(sum_with_single_dependency, result)
 end