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diff --git a/src/de/lmu/ifi/dbs/elki/math/linearalgebra/EigenPair.java b/src/de/lmu/ifi/dbs/elki/math/linearalgebra/EigenPair.java
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+++ b/src/de/lmu/ifi/dbs/elki/math/linearalgebra/EigenPair.java
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+package de.lmu.ifi.dbs.elki.math.linearalgebra;
+/*
+This file is part of ELKI:
+Environment for Developing KDD-Applications Supported by Index-Structures
+
+Copyright (C) 2011
+Ludwig-Maximilians-Universität München
+Lehr- und Forschungseinheit für Datenbanksysteme
+ELKI Development Team
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU Affero General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU Affero General Public License for more details.
+
+You should have received a copy of the GNU Affero General Public License
+along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+import de.lmu.ifi.dbs.elki.utilities.FormatUtil;
+
+/**
+ * Helper class which encapsulates an eigenvector and its corresponding
+ * eigenvalue. This class is used to sort eigenpairs.
+ * 
+ * @author Elke Achtert
+ * 
+ * @apiviz.composedOf Matrix
+ */
+public class EigenPair implements Comparable<EigenPair> {
+  /**
+   * The eigenvector as a matrix.
+   */
+  private Vector eigenvector;
+
+  /**
+   * The corresponding eigenvalue.
+   */
+  private double eigenvalue;
+
+  /**
+   * Creates a new EigenPair object.
+   * 
+   * @param eigenvector the eigenvector as a matrix
+   * @param eigenvalue the corresponding eigenvalue
+   */
+  public EigenPair(Vector eigenvector, double eigenvalue) {
+    this.eigenvalue = eigenvalue;
+    this.eigenvector = eigenvector;
+  }
+
+  /**
+   * Compares this object with the specified object for order. Returns a
+   * negative integer, zero, or a positive integer as this object's eigenvalue
+   * is greater than, equal to, or less than the specified object's eigenvalue.
+   * 
+   * @param o the Eigenvector to be compared.
+   * @return a negative integer, zero, or a positive integer as this object's
+   *         eigenvalue is greater than, equal to, or less than the specified
+   *         object's eigenvalue.
+   */
+  @Override
+  public int compareTo(EigenPair o) {
+    if(this.eigenvalue < o.eigenvalue) {
+      return -1;
+    }
+    if(this.eigenvalue > o.eigenvalue) {
+      return +1;
+    }
+    return 0;
+  }
+
+  /**
+   * Returns the eigenvector.
+   * 
+   * @return the eigenvector
+   */
+  public Vector getEigenvector() {
+    return eigenvector;
+  }
+
+  /**
+   * Returns the eigenvalue.
+   * 
+   * @return the eigenvalue
+   */
+  public double getEigenvalue() {
+    return eigenvalue;
+  }
+
+  /**
+   * Returns a string representation of this EigenPair.
+   * 
+   * @return a string representation of this EigenPair
+   */
+  @Override
+  public String toString() {
+    return "(ew = " + FormatUtil.format(eigenvalue) + ", ev = [" + FormatUtil.format(eigenvector) + "])";
+  }
+}
+\ No newline at end of file