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A fast and easy to use dense and sparse matrix linear algebra library written in Java.
There is a newer version: 0.43.1
/*
 * Copyright (c) 2009-2017, 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.dense.row.decompose;

import org.ejml.data.CMatrixRMaj;
import org.ejml.dense.row.CommonOps_CDRM;

/**
 * Helper functions for generic decompsotions.
 *
 * @author Peter Abeles
 */
public class UtilDecompositons_CDRM {

    public static CMatrixRMaj checkIdentity(CMatrixRMaj A, int numRows, int numCols) {
        if( A == null ) {
            return CommonOps_CDRM.identity(numRows,numCols);
        } else if( numRows != A.numRows || numCols != A.numCols )
            throw new IllegalArgumentException("Input is not "+numRows+" x "+numCols+" matrix");
        else
            CommonOps_CDRM.setIdentity(A);
        return A;
    }

    public static CMatrixRMaj checkZeros(CMatrixRMaj A , int numRows , int numCols) {
        if( A == null ) {
            return new CMatrixRMaj(numRows,numCols);
        } else if( numRows != A.numRows || numCols != A.numCols )
            throw new IllegalArgumentException("Input is not "+numRows+" x "+numCols+" matrix");
        else
            A.zero();
        return A;
    }

    /**
     * Creates a zeros matrix only if A does not already exist.  If it does exist it will fill
     * the lower triangular portion with zeros.
     */
    public static CMatrixRMaj checkZerosLT(CMatrixRMaj A , int numRows , int numCols) {
        if( A == null ) {
            return new CMatrixRMaj(numRows,numCols);
        } else if( numRows != A.numRows || numCols != A.numCols )
            throw new IllegalArgumentException("Input is not "+numRows+" x "+numCols+" matrix");
        else {
            for( int i = 0; i < A.numRows; i++ ) {
                int index = i*A.numCols*2;
                int end = index + Math.min(i,A.numCols)*2;;
                while( index < end ) {
                    A.data[index++] = 0;
                }
            }
        }
        return A;
    }

    /**
     * Creates a zeros matrix only if A does not already exist.  If it does exist it will fill
     * the upper triangular portion with zeros.
     */
    public static CMatrixRMaj checkZerosUT(CMatrixRMaj A , int numRows , int numCols) {
        if( A == null ) {
            return new CMatrixRMaj(numRows,numCols);
        } else if( numRows != A.numRows || numCols != A.numCols )
            throw new IllegalArgumentException("Input is not "+numRows+" x "+numCols+" matrix");
        else {
            int maxRows = Math.min(A.numRows,A.numCols);
            for( int i = 0; i < maxRows; i++ ) {
                int index = (i*A.numCols + i+1)*2;
                int end = (i*A.numCols + A.numCols)*2;
                while( index < end ) {
                    A.data[index++] = 0;
                }
            }
        }
        return A;
    }

}