bug fix (gcc11): comparator must be const (ReferenceSpace)

functionspace/ReferenceSpace.cpp

@@ -253,8 +253,8 @@ bool ReferenceSpace::isSameEdge(const std::vector<size_t>& pTest,
   return match;
 }
 
-bool ReferenceSpace::EdgeComparator::operator()(const std::vector<size_t>& a,
-                                                const std::vector<size_t>& b){
+bool ReferenceSpace::EdgeComparator::operator()(const vector<size_t>& a,
+                                                const vector<size_t>& b) const{
   size_t maxA, minA;
   size_t maxB, minB;
 

functionspace/ReferenceSpace.h

@@ -66,7 +66,7 @@ namespace sf{
     class EdgeComparator{
     public:
       bool operator()(const std::vector<size_t>& a,
-                      const std::vector<size_t>& b);
+                      const std::vector<size_t>& b) const;
     };
 
   private: