Hopefully improve comment about complex/singlecomplex

dune/istl/superlufunctions.hh

@@ -59,8 +59,10 @@ extern "C" {
 
 #if __has_include("slu_cdefs.h")
 #ifndef SUPERLU_TYPEDEF_COMPLEX
-// For now let's keep backwards compatible and let
-// complex be a typedef of doublecomplex
+// Per default SuperLU >= 7.0.0. does not provide
+// a type complex anymore. By setting SUPERLU_TYPEDEF_COMPLEX
+// we tell SuperLU to define complex to be the same as the
+// new type singlecomplex
 #define SUPERLU_TYPEDEF_COMPLEX
 #endif
 #include "slu_scomplex.h"