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#ifndef SMOOTHED_AGGREGATION_H
#define SMOOTHED_AGGREGATION_H
#include <iostream>
#include <vector>
#include <iterator>
#include <assert.h>
//#define DEBUG
template<class T>
void sa_strong_connections(const int n_row,
const T epsilon,
const int Ap[], const int Aj[], const T Ax[],
std::vector<int> * Sp, std::vector<int> * Sj, std::vector<T> * Sx){
//Sp,Sj form a CSR representation where the i-th row contains
//the indices of all the strong connections from node i
Sp->push_back(0);
//compute diagonal values
std::vector<T> diags(n_row);
for(int i = 0; i < n_row; i++){
int row_start = Ap[i];
int row_end = Ap[i+1];
for(int jj = row_start; jj < row_end; jj++){
if(Aj[jj] == i){
diags[i] = Ax[jj];
break;
}
}
}
#ifdef DEBUG
for(int i = 0; i < n_row; i++){ assert(diags[i] > 0); }
#endif
for(int i = 0; i < n_row; i++){
int row_start = Ap[i];
int row_end = Ap[i+1];
T eps_Aii = epsilon*epsilon*diags[i];
for(int jj = row_start; jj < row_end; jj++){
const int& j = Aj[jj];
const T& Aij = Ax[jj];
if(i == j){continue;}
if(Aij*Aij >= eps_Aii * diags[j]){
Sj->push_back(j);
Sx->push_back(Aij);
}
}
Sp->push_back(Sj->size());
}
}
void sa_get_aggregates(const int n_row,
const int Ap[], const int Aj[],
std::vector<int> * Bj){
std::vector<int> aggregates(n_row,-1);
int num_aggregates = 0;
//Pass #1
for(int i = 0; i < n_row; i++){
if(aggregates[i] >= 0){ continue; } //already marked
const int& row_start = Ap[i];
const int& row_end = Ap[i+1];
//Determine whether all neighbors of this node are free (not already aggregates)
bool free_neighborhood = true;
for(int jj = row_start; jj < row_end; jj++){
if(aggregates[Aj[jj]] >= 0){
free_neighborhood = false;
break;
}
}
if(!free_neighborhood){ continue; } //bail out
//Make an aggregate out of this node and its strong neigbors
aggregates[i] = num_aggregates;
for(int jj = row_start; jj < row_end; jj++){
aggregates[Aj[jj]] = num_aggregates;
}
num_aggregates++;
}
//Pass #2
std::vector<int> aggregates_copy(aggregates);
for(int i = 0; i < n_row; i++){
if(aggregates[i] >= 0){ continue; } //already marked
const int& row_start = Ap[i];
const int& row_end = Ap[i+1];
for(int jj = row_start; jj < row_end; jj++){
const int& j = Aj[jj];
if(aggregates_copy[j] >= 0){
aggregates[i] = aggregates_copy[j];
break;
}
}
}
//Pass #3
for(int i = 0; i < n_row; i++){
if(aggregates[i] >= 0){ continue; } //already marked
const int& row_start = Ap[i];
const int& row_end = Ap[i+1];
aggregates[i] = num_aggregates;
for(int jj = row_start; jj < row_end; jj++){
const int& j = Aj[jj];
if(aggregates[j] < 0){ //unmarked neighbors
aggregates[j] = num_aggregates;
}
}
num_aggregates++;
}
#ifdef DEBUG
for(int i = 0; i < n_row; i++){ assert(aggregates[i] >= 0 && aggregates[i] < num_aggregates); }
#endif
*Bj = aggregates;
}
template<class T>
void sa_smoother(const int n_row,
const T omega,
const int Ap[], const int Aj[], const T Ax[],
const int Sp[], const int Sj[], const T Sx[],
std::vector<int> * Bp, std::vector<int> * Bj, std::vector<T> * Bx){
//compute filtered diagonal
std::vector<T> diags(n_row,0);
for(int i = 0; i < n_row; i++){
int row_start = Ap[i];
int row_end = Ap[i+1];
for(int jj = row_start; jj < row_end; jj++){
diags[i] += Ax[jj];
}
}
for(int i = 0; i < n_row; i++){
int row_start = Sp[i];
int row_end = Sp[i+1];
for(int jj = row_start; jj < row_end; jj++){
diags[i] -= Sx[jj];
}
}
#ifdef DEBUG
for(int i = 0; i < n_row; i++){ assert(diags[i] > 0); }
#endif
//compute omega Jacobi smoother
Bp->push_back(0);
for(int i = 0; i < n_row; i++){
int row_start = Sp[i];
int row_end = Sp[i+1];
const T row_scale = -omega/diags[i];
Bx->push_back(1.0);
Bj->push_back( i );
for(int jj = row_start; jj < row_end; jj++){
Bx->push_back(row_scale*Sx[jj]);
Bj->push_back(Sj[jj]);
}
Bp->push_back(Bj->size());
}
}
#endif
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