src/libvpsc/solve_VPSC.cpp

	solve_VPSC.cpp revision aaacc83e3fab3c943e5d3b59646109b6b92c08dd
/**
 * \brief Solve an instance of the "Variable Placement with Separation
 * Constraints" problem.
 *
 * Authors:
 *   Tim Dwyer <tgdwyer@gmail.com>
 *
 * Copyright (C) 2005 Authors
 *
 * Released under GNU LGPL.  Read the file 'COPYING' for more information.
 */

#include <cassert>
#include "constraint.h"
#include "block.h"
#include "blocks.h"
#include "solve_VPSC.h"
#include <math.h>
#include <sstream>
#ifdef RECTANGLE_OVERLAP_LOGGING
#include <fstream>
#endif
#include <map>

using namespace std;

namespace vpsc {

static const double ZERO_UPPERBOUND=-0.0000001;

IncSolver::IncSolver(const unsigned n, Variable* const vs[], const unsigned m, Constraint *cs[])
    : Solver(n,vs,m,cs) {
    inactive.assign(cs,cs+m);
    for(ConstraintList::iterator i=inactive.begin();i!=inactive.end();++i) {
        (*i)->active=false;
    }
}
Solver::Solver(const unsigned n, Variable* const vs[], const unsigned m, Constraint *cs[]) : m(m), cs(cs), n(n), vs(vs) {
    bs=new Blocks(n, vs);
#ifdef RECTANGLE_OVERLAP_LOGGING
    printBlocks();
    //assert(!constraintGraphIsCyclic(n,vs));
#endif
}
Solver::~Solver() {
    delete bs;
}

// useful in debugging
void Solver::printBlocks() {
#ifdef RECTANGLE_OVERLAP_LOGGING
    ofstream f(LOGFILE,ios::app);
    for(set<Block*>::iterator i=bs->begin();i!=bs->end();++i) {
        Block *b=*i;
        f<<"  "<<*b<<endl;
    }
    for(unsigned i=0;i<m;i++) {
        f<<"  "<<*cs[i]<<endl;
    }
#endif
}
/**
* Produces a feasible - though not necessarily optimal - solution by
* examining blocks in the partial order defined by the directed acyclic
* graph of constraints. For each block (when processing left to right) we
* maintain the invariant that all constraints to the left of the block
* (incoming constraints) are satisfied. This is done by repeatedly merging
* blocks into bigger blocks across violated constraints (most violated
* first) fixing the position of variables inside blocks relative to one
* another so that constraints internal to the block are satisfied.
*/
void Solver::satisfy() {
    list<Variable*> *vs=bs->totalOrder();
    for(list<Variable*>::iterator i=vs->begin();i!=vs->end();++i) {
        Variable *v=*i;
        if(!v->block->deleted) {
            bs->mergeLeft(v->block);
        }
    }
    bs->cleanup();
    for(unsigned i=0;i<m;i++) {
        if(cs[i]->slack() < ZERO_UPPERBOUND) {
#ifdef RECTANGLE_OVERLAP_LOGGING
            ofstream f(LOGFILE,ios::app);
            f<<"Error: Unsatisfied constraint: "<<*cs[i]<<endl;
#endif
            //assert(cs[i]->slack()>-0.0000001);
            throw "Unsatisfied constraint";
        }
    }
    delete vs;
}

void Solver::refine() {
    bool solved=false;
    // Solve shouldn't loop indefinately
    // ... but just to make sure we limit the number of iterations
    unsigned maxtries=100;
    while(!solved&&maxtries>0) {
        solved=true;
        maxtries--;
        for(set<Block*>::const_iterator i=bs->begin();i!=bs->end();++i) {
            Block *b=*i;
            b->setUpInConstraints();
            b->setUpOutConstraints();
        }
        for(set<Block*>::const_iterator i=bs->begin();i!=bs->end();++i) {
            Block *b=*i;
            Constraint *c=b->findMinLM();
            if(c!=NULL && c->lm<0) {
#ifdef RECTANGLE_OVERLAP_LOGGING
                ofstream f(LOGFILE,ios::app);
                f<<"Split on constraint: "<<*c<<endl;
#endif
                // Split on c
                Block *l=NULL, *r=NULL;
                bs->split(b,l,r,c);
                bs->cleanup();
                // split alters the block set so we have to restart
                solved=false;
                break;
            }
        }
    }
    for(unsigned i=0;i<m;i++) {
        if(cs[i]->slack() < ZERO_UPPERBOUND) {
            assert(cs[i]->slack()>ZERO_UPPERBOUND);
            throw "Unsatisfied constraint";
        }
    }
}
/**
 * Calculate the optimal solution. After using satisfy() to produce a
 * feasible solution, refine() examines each block to see if further
 * refinement is possible by splitting the block. This is done repeatedly
 * until no further improvement is possible.
 */
void Solver::solve() {
    satisfy();
    refine();
}

void IncSolver::solve() {
#ifdef RECTANGLE_OVERLAP_LOGGING
    ofstream f(LOGFILE,ios::app);
    f<<"solve_inc()..."<<endl;
#endif
    double lastcost,cost = bs->cost();
    do {
        lastcost=cost;
        satisfy();
        splitBlocks();
        cost = bs->cost();
#ifdef RECTANGLE_OVERLAP_LOGGING
    f<<"  cost="<<cost<<endl;
#endif
    } while(fabs(lastcost-cost)>0.0001);
}
/**
 * incremental version of satisfy that allows refinement after blocks are
 * moved.
 *
 *  - move blocks to new positions
 *  - repeatedly merge across most violated constraint until no more
 *    violated constraints exist
 *
 * Note: there is a special case to handle when the most violated constraint
 * is between two variables in the same block.  Then, we must split the block
 * over an active constraint between the two variables.  We choose the
 * constraint with the most negative lagrangian multiplier.
 */
void IncSolver::satisfy() {
#ifdef RECTANGLE_OVERLAP_LOGGING
    ofstream f(LOGFILE,ios::app);
    f<<"satisfy_inc()..."<<endl;
#endif
    splitBlocks();
    long splitCtr = 0;
    Constraint* v = NULL;
    while((v=mostViolated(inactive))&&(v->equality || v->slack() < ZERO_UPPERBOUND)) {
        assert(!v->active);
        Block *lb = v->left->block, *rb = v->right->block;
        if(lb != rb) {
            lb->merge(rb,v);
        } else {
            if(lb->isActiveDirectedPathBetween(v->right,v->left)) {
                // cycle found, relax the violated, cyclic constraint
                v->gap = v->slack();
                continue;
            }
            if(splitCtr++>10000) {
                throw "Cycle Error!";
            }
            // constraint is within block, need to split first
            inactive.push_back(lb->splitBetween(v->left,v->right,lb,rb));
            lb->merge(rb,v);
            bs->insert(lb);
        }
    }
#ifdef RECTANGLE_OVERLAP_LOGGING
    f<<"  finished merges."<<endl;
#endif
    bs->cleanup();
    for(unsigned i=0;i<m;i++) {
        v=cs[i];
        if(v->slack() < ZERO_UPPERBOUND) {
            ostringstream s;
            s<<"Unsatisfied constraint: "<<*v;
#ifdef RECTANGLE_OVERLAP_LOGGING
            ofstream f(LOGFILE,ios::app);
            f<<s.str()<<endl;
#endif
            throw s.str().c_str();
        }
    }
#ifdef RECTANGLE_OVERLAP_LOGGING
    f<<"  finished cleanup."<<endl;
    printBlocks();
#endif
}
void IncSolver::moveBlocks() {
#ifdef RECTANGLE_OVERLAP_LOGGING
    ofstream f(LOGFILE,ios::app);
    f<<"moveBlocks()..."<<endl;
#endif
    for(set<Block*>::const_iterator i(bs->begin());i!=bs->end();++i) {
        Block *b = *i;
        b->wposn = b->desiredWeightedPosition();
        b->posn = b->wposn / b->weight;
    }
#ifdef RECTANGLE_OVERLAP_LOGGING
    f<<"  moved blocks."<<endl;
#endif
}
void IncSolver::splitBlocks() {
#ifdef RECTANGLE_OVERLAP_LOGGING
    ofstream f(LOGFILE,ios::app);
#endif
    moveBlocks();
    splitCnt=0;
    // Split each block if necessary on min LM
    for(set<Block*>::const_iterator i(bs->begin());i!=bs->end();++i) {
        Block* b = *i;
        Constraint* v=b->findMinLM();
        if(v!=NULL && v->lm < ZERO_UPPERBOUND) {
            assert(!v->equality);
#ifdef RECTANGLE_OVERLAP_LOGGING
            f<<"    found split point: "<<*v<<" lm="<<v->lm<<endl;
#endif
            splitCnt++;
            Block *b = v->left->block, *l=NULL, *r=NULL;
            assert(v->left->block == v->right->block);
            double pos = b->posn;
            b->split(l,r,v);
            l->posn=r->posn=pos;
            l->wposn = l->posn * l->weight;
            r->wposn = r->posn * r->weight;
            bs->insert(l);
            bs->insert(r);
            b->deleted=true;
            inactive.push_back(v);
#ifdef RECTANGLE_OVERLAP_LOGGING
            f<<"  new blocks: "<<*l<<" and "<<*r<<endl;
#endif
        }
    }
#ifdef RECTANGLE_OVERLAP_LOGGING
    f<<"  finished splits."<<endl;
#endif
    bs->cleanup();
}

/**
 * Scan constraint list for the most violated constraint, or the first equality
 * constraint
 */
Constraint* IncSolver::mostViolated(ConstraintList &l) {
    double minSlack = DBL_MAX;
    Constraint* v=NULL;
#ifdef RECTANGLE_OVERLAP_LOGGING
    ofstream f(LOGFILE,ios::app);
    f<<"Looking for most violated..."<<endl;
#endif
    ConstraintList::iterator end = l.end();
    ConstraintList::iterator deletePoint = end;
    for(ConstraintList::iterator i=l.begin();i!=end;++i) {
        Constraint *c=*i;
        double slack = c->slack();
        if(c->equality || slack < minSlack) {
            minSlack=slack;
            v=c;
            deletePoint=i;
            if(c->equality) break;
        }
    }
    // Because the constraint list is not order dependent we just
    // move the last element over the deletePoint and resize
    // downwards.  There is always at least 1 element in the
    // vector because of search.
    if(deletePoint != end && (minSlack<ZERO_UPPERBOUND||v->equality)) {
        *deletePoint = l[l.size()-1];
        l.resize(l.size()-1);
    }
#ifdef RECTANGLE_OVERLAP_LOGGING
    f<<"  most violated is: "<<*v<<endl;
#endif
    return v;
}

struct node {
    set<node*> in;
    set<node*> out;
};
// useful in debugging - cycles would be BAD
bool Solver::constraintGraphIsCyclic(const unsigned n, Variable* const vs[]) {
    map<Variable*, node*> varmap;
    vector<node*> graph;
    for(unsigned i=0;i<n;i++) {
        node *u=new node;
        graph.push_back(u);
        varmap[vs[i]]=u;
    }
    for(unsigned i=0;i<n;i++) {
        for(vector<Constraint*>::iterator c=vs[i]->in.begin();c!=vs[i]->in.end();++c) {
            Variable *l=(*c)->left;
            varmap[vs[i]]->in.insert(varmap[l]);
        }

        for(vector<Constraint*>::iterator c=vs[i]->out.begin();c!=vs[i]->out.end();++c) {
            Variable *r=(*c)->right;
            varmap[vs[i]]->out.insert(varmap[r]);
        }
    }
    while(graph.size()>0) {
        node *u=NULL;
        vector<node*>::iterator i=graph.begin();
        for(;i!=graph.end();++i) {
            u=*i;
            if(u->in.size()==0) {
                break;
            }
        }
        if(i==graph.end() && graph.size()>0) {
            //cycle found!
            return true;
        } else {
            graph.erase(i);
            for(set<node*>::iterator j=u->out.begin();j!=u->out.end();++j) {
                node *v=*j;
                v->in.erase(u);
            }
            delete u;
        }
    }
    for(unsigned i=0; i<graph.size(); ++i) {
        delete graph[i];
    }
    return false;
}

// useful in debugging - cycles would be BAD
bool Solver::blockGraphIsCyclic() {
    map<Block*, node*> bmap;
    vector<node*> graph;
    for(set<Block*>::const_iterator i=bs->begin();i!=bs->end();++i) {
        Block *b=*i;
        node *u=new node;
        graph.push_back(u);
        bmap[b]=u;
    }
    for(set<Block*>::const_iterator i=bs->begin();i!=bs->end();++i) {
        Block *b=*i;
        b->setUpInConstraints();
        Constraint *c=b->findMinInConstraint();
        while(c!=NULL) {
            Block *l=c->left->block;
            bmap[b]->in.insert(bmap[l]);
            b->deleteMinInConstraint();
            c=b->findMinInConstraint();
        }

        b->setUpOutConstraints();
        c=b->findMinOutConstraint();
        while(c!=NULL) {
            Block *r=c->right->block;
            bmap[b]->out.insert(bmap[r]);
            b->deleteMinOutConstraint();
            c=b->findMinOutConstraint();
        }
    }
    while(graph.size()>0) {
        node *u=NULL;
        vector<node*>::iterator i=graph.begin();
        for(;i!=graph.end();++i) {
            u=*i;
            if(u->in.size()==0) {
                break;
            }
        }
        if(i==graph.end() && graph.size()>0) {
            //cycle found!
            return true;
        } else {
            graph.erase(i);
            for(set<node*>::iterator j=u->out.begin();j!=u->out.end();++j) {
                node *v=*j;
                v->in.erase(u);
            }
            delete u;
        }
    }
    for(unsigned i=0; i<graph.size(); i++) {
        delete graph[i];
    }
    return false;
}
}