update doc snippets
diff --git a/doc/snippets/LU_image.cpp b/doc/snippets/LU_image.cpp
index 0d1088a..d3092e8 100644
--- a/doc/snippets/LU_image.cpp
+++ b/doc/snippets/LU_image.cpp
@@ -6,4 +6,4 @@
 cout << "Notice that the middle column is the sum of the two others, so the "
      << "columns are linearly dependent." << endl;
 cout << "Here is a matrix whose columns have the same span but are linearly independent:"
-     << endl << m.lu().image() << endl;
+     << endl << m.lu().image(m) << endl;