From cf6f2af2e85a8f370dc5a4fd2d0adb33d77b2b6a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Sergio=20S=C3=A1nchez=20Ram=C3=ADrez?=
 <sergio.sanchez.ramirez+git@bsc.es>
Date: Thu, 18 Jan 2024 19:16:43 +0100
Subject: [PATCH] Ignore outer products in `Exhaustive` breadth-first search

---
 src/Optimizers/Exhaustive.jl | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/Optimizers/Exhaustive.jl b/src/Optimizers/Exhaustive.jl
index 424ada2..7c6ba78 100644
--- a/src/Optimizers/Exhaustive.jl
+++ b/src/Optimizers/Exhaustive.jl
@@ -75,7 +75,6 @@ function exhaustive_breadthfirst(
     outer::Bool = false,
     hashyperinds = !isempty(hyperinds(expr)),
 ) where {L,Metric}
-    outer && error("Outer products not supported yet")
     hashyperinds && error("Hyperindices not supported yet")
 
     cost_fac = maximum(values(expr.size))
@@ -119,7 +118,8 @@ function exhaustive_breadthfirst(
             # if not disjoint, then ta and tb contain at least one common tensor
             isdisjoint(ta, tb) || continue
 
-            get(costs, ta ∪ tb, cost_cur) > cost_prev || continue
+            # outer products do not generally improve contraction path
+            !outer && isdisjoint(indices[ta], indices[tb]) && continue
 
             # new candidate contraction
             tc = ta ∪ tb # aka Q in the paper