001/*
002 * $Id$
003 */
004
005package edu.jas.gb;
006
007
008import java.util.List;
009
010import org.apache.logging.log4j.Logger;
011import org.apache.logging.log4j.LogManager; 
012
013import edu.jas.poly.GenWordPolynomial;
014import edu.jas.poly.GenWordPolynomialRing;
015import edu.jas.poly.PolyUtil;
016import edu.jas.structure.RingElem;
017
018
019/**
020 * Non-commutative word Groebner Base sequential algorithm. Implements Groebner
021 * bases and GB test.
022 * @param <C> coefficient type
023 * @author Heinz Kredel
024 */
025
026public class WordGroebnerBaseSeq<C extends RingElem<C>> extends WordGroebnerBaseAbstract<C> {
027
028
029    private static final Logger logger = LogManager.getLogger(WordGroebnerBaseSeq.class);
030
031
032    private static final boolean debug = logger.isDebugEnabled();
033
034
035    /**
036     * Constructor.
037     */
038    public WordGroebnerBaseSeq() {
039        super();
040    }
041
042
043    /**
044     * Constructor.
045     * @param red Reduction engine
046     */
047    public WordGroebnerBaseSeq(WordReduction<C> red) {
048        super(red);
049    }
050
051
052    /**
053     * Constructor.
054     * @param red Reduction engine
055     * @param pl pair selection strategy
056     */
057    public WordGroebnerBaseSeq(WordReduction<C> red, WordPairList<C> pl) {
058        super(red, pl);
059    }
060
061
062    /**
063     * Word Groebner base using word pairlist class.
064     * @param F word polynomial list.
065     * @return GB(F) a finite non-commutative Groebner base of F, if it exists.
066     */
067    @Override
068    public List<GenWordPolynomial<C>> GB(List<GenWordPolynomial<C>> F) {
069        List<GenWordPolynomial<C>> G = normalizeZerosOnes(F);
070        G = PolyUtil.<C> wordMonic(G);
071        if (G.size() <= 1) {
072            return G;
073        }
074        GenWordPolynomialRing<C> ring = G.get(0).ring;
075        if (!ring.coFac.isField()) {
076            throw new IllegalArgumentException("coefficients not from a field");
077        }
078        //Collections.sort(G);
079        OrderedWordPairlist<C> pairlist = (OrderedWordPairlist<C>) strategy.create(ring);
080        pairlist.put(G);
081        logger.info("start {}", pairlist);
082
083        WordPair<C> pair;
084        GenWordPolynomial<C> pi;
085        GenWordPolynomial<C> pj;
086        List<GenWordPolynomial<C>> S;
087        GenWordPolynomial<C> H;
088        while (pairlist.hasNext()) {
089            pair = pairlist.removeNext();
090            //logger.debug("pair = {}", pair);
091            if (pair == null) {
092                continue;
093            }
094            pi = pair.pi;
095            pj = pair.pj;
096            if (debug) {
097                logger.info("pi   = {}, pj = {}", pi, pj);
098            }
099
100            S = red.SPolynomials(pi, pj);
101            if (S.isEmpty()) {
102                continue;
103            }
104            for (GenWordPolynomial<C> s : S) {
105                if (s.isZERO()) {
106                    //pair.setZero();
107                    continue;
108                }
109                if (debug) {
110                    logger.info("ht(S) = {}", s.leadingWord());
111                }
112                boolean t = pairlist.criterion3(pair.i, pair.j, s.leadingWord());
113                //System.out.println("criterion3(" + pair.i + "," + pair.j + ") = " + t);
114                //if ( !t ) {
115                //    continue;  
116                //}
117
118                H = red.normalform(G, s);
119                if (debug) {
120                    //logger.info("pair = {}", pair);
121                    //logger.info("ht(S) = {}", S.monic()); //.leadingWord() );
122                    logger.info("ht(H) = {}", H.monic()); //.leadingWord() );
123                }
124                if (H.isZERO()) {
125                    //pair.setZero();
126                    continue;
127                }
128                if (!t) {
129                    logger.info("criterion3({},{}) wrong: {} --> {}", pair.i, pair.j, s.leadingWord(), H.leadingWord());
130                }
131
132                H = H.monic();
133                if (debug) {
134                    logger.info("ht(H) = {}", H.leadingWord());
135                }
136                if (H.isONE()) {
137                    G.clear();
138                    G.add(H);
139                    return G; // since no threads are activated
140                }
141                if (debug) {
142                    logger.info("H = {}", H);
143                }
144                if (H.length() > 0) {
145                    //l++;
146                    G.add(H);
147                    pairlist.put(H);
148                }
149            }
150        }
151        //logger.info("#sequential list = {}", G.size());
152        G = minimalGB(G);
153        logger.info("end   {}", pairlist);
154        //Collections.sort(G);
155        //Collections.reverse(G);
156        return G;
157    }
158
159}