From 3da3efa57c002139edb1878eec70f5f170cb4197 Mon Sep 17 00:00:00 2001
From: Jiri Pittner <jiri@pittnerovi.com>
Date: Thu, 20 Nov 2025 21:00:33 +0100
Subject: [PATCH] tensor: improved diagnostics

---
 t.cc     | 1 +
 tensor.h | 8 +++++++-
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/t.cc b/t.cc
index 318a52a..b5f17c5 100644
--- a/t.cc
+++ b/t.cc
@@ -4497,6 +4497,7 @@ for(int i=0; i<n+2; ++i) for(int j=0; j<n+2; ++j) for(int k=0; k<n+2; ++k) for(i
 		y.lhs(i,j,k,l) += x(ii,jj,kk,ll) * t[0](i,ii) * t[0](j,jj) * t[0](k,kk) * t[1](l,ll) ;
 	}
 cout <<"Error = "<<(xt-y).norm()<<endl;
+
 }
 
 }//main
diff --git a/tensor.h b/tensor.h
index 29ab57c..7b6d379 100644
--- a/tensor.h
+++ b/tensor.h
@@ -84,10 +84,16 @@ if(LA_traits<T>::is_complex()) //condition known at compile time
 }
 
 
+static bool didwarn=false;
 static inline bool ptr_ok(void *ptr)
 {
 #ifdef DEBUG
-if(ptr==NULL) std::cout<<"Warning: write to nonexistent tensor element ignored\n";
+if(ptr==NULL && !didwarn) 
+	{
+	std::cout<<"Warning: write to zero element of antisym tensor ignored\n";
+	std::cerr<<"Warning: write to zero element of antisym tensor ignored\n";
+	didwarn=true;
+	}
 #endif
 return (bool)ptr;
 }