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A fast and easy to use dense and sparse matrix linear algebra library written in Java.
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/*
 * Copyright (c) 2022, 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.data;

import org.ejml.EjmlParameters;

import java.util.Arrays;

/**
 * A row-major block matrix declared on to one continuous array.
 *
 * @author Peter Abeles
 */
public class DMatrixRBlock extends DMatrixD1 {
    public int blockLength;

    public DMatrixRBlock( int numRows, int numCols, int blockLength ) {
        assignShape(numRows, numCols);
        this.data = new double[numRows*numCols];
        this.blockLength = blockLength;
    }

    public DMatrixRBlock( int numRows, int numCols ) {
        this(numRows, numCols, EjmlParameters.BLOCK_WIDTH);
    }

    public DMatrixRBlock() {}

    public void set( DMatrixRBlock A ) {
        this.blockLength = A.blockLength;
        assignShape(A.numRows, A.numCols);

        int N = numCols*numRows;

        if (data.length < N)
            data = new double[N];

        System.arraycopy(A.data, 0, data, 0, N);
    }

    public static DMatrixRBlock wrap( double[] data, int numRows, int numCols, int blockLength ) {
        var ret = new DMatrixRBlock();
        ret.assignShape(numRows, numCols);
        ret.data = data;
        ret.blockLength = blockLength;

        return ret;
    }

    @Override public double[] getData() {
        return data;
    }

    @Override public void reshape( int numRows, int numCols, boolean saveValues ) {
        int numElements = getNumElements();
        assignShape(numRows, numCols);
        if (data.length < numRows*numCols) {
            var data = new double[numRows*numCols];

            if (saveValues) {
                System.arraycopy(this.data, 0, data, 0, numElements);
            }

            this.data = data;
        }
    }

    public void reshape( int numRows, int numCols, int blockLength, boolean saveValues ) {
        this.blockLength = blockLength;
        this.reshape(numRows, numCols, saveValues);
    }

    @Override public int getIndex( int row, int col ) {
        // find the block it is inside
        int blockRow = row/blockLength;
        int blockCol = col/blockLength;

        int localHeight = Math.min(numRows - blockRow*blockLength, blockLength);

        int index = blockRow*blockLength*numCols + blockCol*localHeight*blockLength;

        int localLength = Math.min(numCols - blockLength*blockCol, blockLength);

        row = row%blockLength;
        col = col%blockLength;

        return index + localLength*row + col;
    }

    @Override public double get( int row, int col ) {
        return data[getIndex(row, col)];
    }

    @Override public double unsafe_get( int row, int col ) {
        return data[getIndex(row, col)];
    }

    @Override public void set( int row, int col, double val ) {
        data[getIndex(row, col)] = val;
    }

    @Override public void unsafe_set( int row, int col, double val ) {
        data[getIndex(row, col)] = val;
    }

    @Override public int getNumRows() {
        return numRows;
    }

    @Override public int getNumCols() {
        return numCols;
    }

    @Override public void zero() {
        Arrays.fill(data, 0, getNumElements(), 0.0);
    }

    @Override public  T createLike() {
        return (T)new DMatrixRBlock(numRows, numCols, blockLength);
    }

    @Override public  T create( int numRows, int numCols ) {
        return (T)new DMatrixRBlock(numRows, numCols, blockLength);
    }

    @Override public void setTo( Matrix original ) {
        if (original instanceof DMatrixRBlock) {
            set((DMatrixRBlock)original);
        } else {
            DMatrix m = (DMatrix)original;

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

    @Override public DMatrixRBlock copy() {
        DMatrixRBlock A = new DMatrixRBlock(numRows, numCols, blockLength);
        A.set(this);
        return A;
    }

    @Override public MatrixType getType() {
        return MatrixType.UNSPECIFIED;
    }
}