From e7bd7e4e18895c52f8f03a655713920a91bb332d Mon Sep 17 00:00:00 2001
From: conrad <conrad@localhost.localdomain>
Date: Sun, 29 Jun 2025 22:52:33 +1000
Subject: [PATCH] return early if there are no non-zero elements

---
 include/armadillo_bits/fn_accu.hpp | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/include/armadillo_bits/fn_accu.hpp b/include/armadillo_bits/fn_accu.hpp
index 41fcaadc..3b24e0ce 100644
--- a/include/armadillo_bits/fn_accu.hpp
+++ b/include/armadillo_bits/fn_accu.hpp
@@ -1408,6 +1408,8 @@ accu(const SpOp<T1, spop_square>& expr)
     {
     const SpSubview_col<eT>& svcol = reinterpret_cast<const SpSubview_col<eT>&>(expr.m);
     
+    if(svcol.n_nonzero == 0)  { return eT(0); }
+    
     if(svcol.n_rows == svcol.m.n_rows)
       {
       arma_debug_print("accu(): SpSubview_col spop_square optimisation");
@@ -1460,6 +1462,8 @@ accu_spop_omit_helper(const T1& expr, functor is_omitted)
     {
     const SpSubview_col<eT>& svcol = reinterpret_cast<const SpSubview_col<eT>&>(expr);
     
+    if(svcol.n_nonzero == 0)  { return eT(0); }
+    
     if(svcol.n_rows == svcol.m.n_rows)
       {
       arma_debug_print("accu_spop_omit_helper(): SpSubview_col optimisation");