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A fast and easy to use dense matrix linear algebra library written in Java.
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/*
 * Copyright (c) 2009-2013, Peter Abeles. All Rights Reserved.
 *
 * This file is part of Efficient Java Matrix Library (EJML).
 *
 * 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.
 */

package org.ejml.alg.generic;

import org.ejml.data.ReshapeMatrix64F;

import java.util.Random;

/**
 * @author Peter Abeles
 */
public class GenericMatrixOps {

//    public static DenseD2Matrix64F convertToD2( DenseMatrix64F orig ) {
//        DenseD2Matrix64F ret = new DenseD2Matrix64F(orig.numRows,orig.numCols);
//
//        copy(orig,ret);
//
//        return ret;
//    }

    public static boolean isEquivalent( ReshapeMatrix64F a , ReshapeMatrix64F b , double tol )
    {
        if( a.numRows != b.numRows || a.numCols != b.numCols )
            return false;

        for( int i = 0; i < a.numRows; i++ ) {
            for( int j = 0; j < a.numCols; j++ ) {
                double diff = Math.abs(a.get(i,j) - b.get(i,j));

                if( diff > tol )
                    return false;
            }
        }

        return true;
    }

    /**
     * Returns true if the provided matrix is has a value of 1 along the diagonal
     * elements and zero along all the other elements.
     *
     * @param a Matrix being inspected.
     * @param tol How close to zero or one each element needs to be.
     * @return If it is within tolerance to an identity matrix.
     */
    public static boolean isIdentity( ReshapeMatrix64F a , double tol )
    {
        for( int i = 0; i < a.numRows; i++ ) {
            for( int j = 0; j < a.numCols; j++ ) {
                if( i == j ) {
                    if( Math.abs(a.get(i,j)-1.0) > tol )
                        return false;
                } else {
                    if( Math.abs(a.get(i,j)) > tol )
                        return false;
                }
            }
        }
        return true;
    }

    public static boolean isEquivalentTriangle( boolean upper , ReshapeMatrix64F a , ReshapeMatrix64F b , double tol )
    {
        if( a.numRows != b.numRows || a.numCols != b.numCols )
            return false;

        if( upper ) {
            for( int i = 0; i < a.numRows; i++ ) {
                for( int j = i; j < a.numCols; j++ ) {
                    double diff = Math.abs(a.get(i,j) - b.get(i,j));

                    if( diff > tol )
                        return false;
                }
            }
        } else {
            for( int j = 0; j < a.numCols; j++ ) {
                for( int i = j; i < a.numRows; i++ ) {
                    double diff = Math.abs(a.get(i,j) - b.get(i,j));

                    if( diff > tol )
                        return false;
                }
            }
        }

        return true;
    }

    public static void copy( ReshapeMatrix64F from , ReshapeMatrix64F to )
    {
        int numCols = from.getNumCols();
        int numRows = from.getNumRows();

        for( int i = 0; i < numRows; i++ ) {
            for( int j = 0; j < numCols; j++ ) {
                to.set(i,j,from.get(i,j));
            }
        }
    }

    public static void setRandom( ReshapeMatrix64F a , double min , double max , Random rand )
    {
        for( int i = 0; i < a.numRows; i++ ) {
            for( int j = 0; j < a.numCols; j++ ) {
                double val = rand.nextDouble()*(max-min)+min;
                a.set(i,j,val);
            }
        }
    }
}