Fixed an indexing bug

include/system.hpp

@@ -72,6 +72,8 @@ class System{
 
                 //Calculates dynamical matrix for the currently pushed values
                 void calculate_matrix(const matelecalc_t& mec){
+                        //for convenience
+                        size_t N = drums_.size()-1;
                         //clear the matrix
                         matrix_.clear();
                         //prepare memory
@@ -85,14 +87,14 @@ class System{
                                 size_t n1_index = sysparams_.adjacency_vector[i][1];
                                 size_t n2_index = sysparams_.adjacency_vector[i][2];
                                 //diagonal
-                                matrix_[i][i] = mec(i, drums_);
+                                matrix_[N*i + i] = mec(i, drums_);
                                 //couplings
                                 if(n0_index != drums_.size()-1) [[likely]] //actually a neighbour
-                                        matrix_[i][n0_index] = mec(i, n0_index, drums_);
+                                        matrix_[N*i + n0_index] = mec(i, n0_index, drums_);
                                 if(n1_index != drums_.size()-1) [[likely]] //actually a neighbour
-                                        matrix_[i][n1_index] = mec(i, n1_index, drums_);
+                                        matrix_[N*i + n1_index] = mec(i, n1_index, drums_);
                                 if(n2_index != drums_.size()-1) [[likely]] //actually a neighbour
-                                        matrix_[i][n2_index] = mec(i, n2_index, drums_);
+                                        matrix_[N*i + n2_index] = mec(i, n2_index, drums_);
                         }
                 }