void Permutation::invert(Permutation& result) const {
// Rem: this is coherent with the convention
// size()==0 <=> this is the identity permutation
result.allocate(size()) ;
for(index_t i=0; i<size(); i++) {
result[(*this)[i]] = i ;
}
}
static void compute_permutation(const SparseMatrix& A, Permutation& permutation) {
permutation.allocate(A.n()) ;
bool RCMK = false ;
if(RCMK) {
SparseMatrixPatternCRS A_pattern ;
::OGF::convert_matrix(A, A_pattern) ;
A_pattern.compute_RCMK_ordering(permutation) ;
if(true) {
std::cerr << "Bandwidth before permutation: " << A_pattern.bandwidth() << std::endl ;
SparseMatrixCRS<double> A_crs ;
::OGF::convert_matrix(A, A_crs, true, permutation) ;
std::cerr << "Bandwidth after permutation: " << A_crs.bandwidth() << std::endl ;
}
} else {
permutation.load_identity() ;
}
}
void SparseMatrixPatternCRS::compute_RCMK_ordering(Permutation& result) {
gx_assert(m() == n()) ;
if(symmetric_storage) {
std::cerr << "RCMK: Expanding symmetric storage" << std::endl ;
SparseMatrixPatternCRS temp ;
expand_symmetric_pattern(temp) ;
temp.compute_RCMK_ordering(result) ;
return ;
}
index_t cur_id = n()-1 ;
result.allocate(n()) ;
result.set_all(NO_INDEX) ;
Permutation dist ;
dist.allocate(n()) ;
// Note: the graph of the matrix may
// have multiple connected component,
// therefore we need this outer loop.
for(index_t x=0; x<n(); x++) {
if(result[x] != NO_INDEX) { continue ; }
std::deque<index_t> Q ;
signed_index_t r ;
while((r = find_furthest_node(x, dist)) != -1) { x = r ; }
index_t seed = x ;
Q.push_back(seed) ;
result[seed] = cur_id-- ;
while(!Q.empty()) {
index_t cur = Q.front() ;
Q.pop_front() ;
std::vector<index_t> neighbors ;
for(index_t jj=rowptr[cur]; jj < rowptr[cur+1]; jj++) {
index_t j = colind[jj] ;
if(result[j] == NO_INDEX) {
neighbors.push_back(j) ;
}
}
std::sort(neighbors.begin(), neighbors.end(), CompareDegree(this)) ;
for(index_t k=0; k<neighbors.size(); k++) {
index_t nn = neighbors[k] ;
result[nn] = cur_id-- ;
Q.push_back(nn) ;
}
}
}
// sanity check
for(index_t i=0; i<n(); i++) {
if(result[i] == NO_INDEX) {
result[i] = cur_id-- ;
}
}
}
