breeze.optimize.linear.CompetitiveLinking.scala Maven / Gradle / Ivy
package breeze.optimize.linear
/*
Copyright 2010 David Hall, Daniel Ramage
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/
import collection.mutable.BitSet;
object CompetitiveLinking extends BipartiteMatching {
/**
* Performs greedy bipartite matching (aka competitive linking). Finds min matches
* @param matchingPotentials matrix, m >= n
* @return matching of size n, with values in 0..m-1, along with the score of the matching
*/
def extractMatching(matchingPotentials: Seq[Seq[Double]]):(Seq[Int],Double) = {
val n = matchingPotentials.length;
val m = matchingPotentials(0).length;
require (m >= n, "Column dimension must be at least the size of row dim.");
val predsIt = for( (arr,i) <- matchingPotentials.iterator.zipWithIndex;
(w,j) <- arr.iterator.zipWithIndex) yield Prediction(i,j,w);
val preds = predsIt.toSeq.sortWith(_.v < _.v);
val leftSet = new BitSet(n);
val rightSet = new BitSet(m);
val matching = Array.fill(n)(-1);
var score = 0.0;
for (pred <- preds.iterator.takeWhile(_ => leftSet.size < n || rightSet.size < m);
if !leftSet(pred.i) && !rightSet(pred.j)) {
matching(pred.i) = pred.j;
leftSet.add(pred.i);
rightSet.add(pred.j);
score += pred.v;
}
matching foreach { a => assert(a >= 0) };
(matching,score);
}
private case class Prediction(i: Int, j: Int, v: Double);
}