/*
* lahiri()
* - implements the NCD-UTVPI() algorithm from An Efficient Decision Procedure for UTVPI Constraints - Lahiri, Musuvathi
* - calls johnsonAllPairs(), into which the Model Generation algorithm from this paper was integrated, in order to significantly
* reduce the space complexity of this implementation
* - if the system is found to be integrally infeasible, returns a pointer to a ConstraintRefList storing a proof of this
* - otherwise, returns NULL
*
* Gphi - pointer to the overall System struct containing the graph representation
*/
static ConstraintRefList * lahiri(System * Gphi){
System GphiPrime;
onlySlacklessEdges(Gphi, &GphiPrime);
stronglyConnectedComponents(&GphiPrime);
int infeasibleVertexIndex = -1;
for(int i = 0; i < Gphi->n && infeasibleVertexIndex < 0; i++){
if( GphiPrime.graph[POSITIVE][i].sccNumber == GphiPrime.graph[NEGATIVE][i].sccNumber
&& ( Gphi->graph[POSITIVE][i].D - Gphi->graph[NEGATIVE][i].D ) % 2 != 0 ){
infeasibleVertexIndex = i;
}
}
if( infeasibleVertexIndex >= 0 ){
ConstraintRefList * infeasibilityProof = generateProof(Gphi, &GphiPrime, infeasibleVertexIndex);
freeSystem( &GphiPrime );
return infeasibilityProof;
}
freeSystem( &GphiPrime );
setSystemForJohnson( Gphi );
johnsonAllPairs( Gphi );
return NULL;
}
const BaseMath &
BaseMath::writeStrongComponents( std::ostream & os ) const {
typedef InputGraph Graph;
auto const & g = this->_input_graph;
Graph::NodeMap< int > component_id(g);
const int n_components = stronglyConnectedComponents( g, component_id );
std::vector< int > component_size( n_components, 0 );
std::vector< int > component_non_dummy_size( n_components, 0 );
/**
* Iterate all nodes, get the component id,
* update the size.
*/
for ( Graph::NodeIt n(g); n != lemon::INVALID; ++ n ) {
++ component_size[ component_id[n] ];
if ( !_dummy[n] ) {
++ component_non_dummy_size[ component_id[n] ];
}
}
os << "Strongly connected components of input graph = " << n_components << std::endl;
os << "Component sizes =";
for ( auto n : component_size ) {
os << " " << n;
}
os << std::endl;
os << "Component sizes (non-dummy) =";
for ( auto n : component_non_dummy_size ) {
os << " " << n;
}
os << std::endl;
return *this;
}
