///////////////////////////////////////////////////////////////////////////////
// For information as to what this class does, see the Javadoc, below.       //
// Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006,       //
// 2007, 2008, 2009, 2010, 2014, 2015 by Peter Spirtes, Richard Scheines, Joseph   //
// Ramsey, and Clark Glymour.                                                //
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// GNU General Public License for more details.                              //
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// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA //
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package edu.cmu.tetrad.util;

import cern.colt.matrix.DoubleMatrix1D;
import cern.colt.matrix.DoubleMatrix2D;
import cern.colt.matrix.impl.DenseDoubleMatrix1D;
import cern.colt.matrix.impl.DenseDoubleMatrix2D;
import cern.colt.matrix.linalg.CholeskyDecomposition;

/**
 * Sundry utilities for the Ling algorithm.
 */
public class LingUtils {
    //Gustavo 7 May 2007
    //
    //makes the diagonal 1, scaling the remainder of each row appropriately
    //pre: 'matrix' must be square
    public static TetradMatrix normalizeDiagonal(TetradMatrix matrix) {
        TetradMatrix resultMatrix = matrix.copy();
        for (int i = 0; i < resultMatrix.rows(); i++) {
            double factor = 1 / resultMatrix.get(i, i);
            for (int j = 0; j < resultMatrix.columns(); j++)
                resultMatrix.set(i, j, factor * resultMatrix.get(i, j));
        }
        return resultMatrix;
    }

    public static boolean isPositiveDefinite(TetradMatrix matrix) {
        return new CholeskyDecomposition(new DenseDoubleMatrix2D(matrix.toArray())).isSymmetricPositiveDefinite();
    }

}