Lanczos untested/partially tested additions. In middle of shake out but at least compiles

lib/algorithms/iterative/EigenSort.h

@@ -0,0 +1,52 @@
+#ifndef GRID_EIGENSORT_H
+#define GRID_EIGENSORT_H
+
+
+namespace Grid {
+    /////////////////////////////////////////////////////////////
+    // Eigen sorter to begin with
+    /////////////////////////////////////////////////////////////
+
+template<class Field>
+class SortEigen {
+ private:
+  
+  static bool less_lmd(RealD left,RealD right){
+    return fabs(left) < fabs(right);
+  }  
+  static bool less_pair(std::pair<RealD,Field>& left,
+		 std::pair<RealD,Field>& right){
+    return fabs(left.first) < fabs(right.first);
+  }  
+  
+ public:
+
+  void push(DenseVector<RealD>& lmd,
+	    DenseVector<Field>& evec,int N) {
+
+    DenseVector<std::pair<RealD, Field> > emod;
+    typename DenseVector<std::pair<RealD, Field> >::iterator it;
+    
+    for(int i=0;i<lmd.size();++i){
+      emod.push_back(std::pair<RealD,Field>(lmd[i],evec[i]));
+    }
+
+    partial_sort(emod.begin(),emod.begin()+N,emod.end(),less_pair);
+
+    it=emod.begin();
+    for(int i=0;i<N;++i){
+      lmd[i]=it->first;
+      evec[i]=it->second;
+      ++it;
+    }
+  }
+  void push(DenseVector<RealD>& lmd,int N) {
+    std::partial_sort(lmd.begin(),lmd.begin()+N,lmd.end(),less_lmd);
+  }
+  bool saturated(RealD lmd, RealD thrs) {
+    return fabs(lmd) > fabs(thrs);
+  }
+};
+
+}
+#endif