JAVA学习（小白向）—矩阵相乘—2021-05-27

JAVA学习（小白向）—矩阵相乘—2021-05-27

矩阵乘法的定义
代码如下：

package a8;

import java.util.Arrays;

/**
 * 
 * @author hengyuzuo
 *
 */
public class MatrixM {
	/**
	 * **********************
	 * The entrance of the program.
	 * 
	 * @param args Not used now.
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		matrixMultiplicationTest();
	}// Of main
	
	/**
	 * **********************
	 * Unit test for respective method.
	 * **********************
	 */
	
	public static void matrixMultiplicationTest() {
		int[][] tempMatrix1 = new int[2][3];
		for (int i = 0; i < tempMatrix1.length; i++) {
			for (int j =0; j < tempMatrix1[0].length; j++) {
				tempMatrix1[i][j] = i + j;
				/**
				 * 0.1.2
				 * 1.2.3
				 * 
				 */
			}// Of for j
		}// Of for i
		
		System.out.println("The first matrix is: " + Arrays.deepToString(tempMatrix1));
		
		int[][] tempMatrix2 = new int[3][4];
		for (int i = 0; i < tempMatrix2.length; i++) {
			for (int j =0; j < tempMatrix2[0].length; j++) {
				tempMatrix2[i][j] = i * 2 + j;
				/**
				 * 0.1.2.3
				 * 2.3.4.5
				 * 4.5.6.7
				 * 
				 */
			}// Of for j
		}// Of for i
		
		System.out.println("The Second matrix is: " + Arrays.deepToString(tempMatrix2));
		
		int[][] tempMatrix3 = multiplication(tempMatrix1, tempMatrix2);
		
		System.out.println("The Third matrix is: " + Arrays.deepToString(tempMatrix3));
		System.out.println("Trying to multiply the first matrix with itself.");
		tempMatrix3 =multiplication(tempMatrix1, tempMatrix1);
		System.out.println("The matrix multiply with itself is: " + Arrays.deepToString(tempMatrix3));
	}// Of matrixMultiplicationTest
	
	/**
	 * *************************************
	 * Matrix multiplication
	 * @param paraMatrix1
	 * @param paraMatrix2
	 * @return the result matrix of multiplication
	 * *************************************
	 */

	public static int[][] multiplication(int[][] paraMatrix1, int[][] paraMatrix2) {
		// TODO Auto-generated method stub
		int m = paraMatrix1.length;
		int n = paraMatrix1[0].length;
		int p = paraMatrix2[0].length;
		
		//Step1.Dimension check
		if (paraMatrix2.length != n) {
			System.out.println("The two matrices cannot be multiplied.");
			return null;		
		}// Of if
		
		//Step2. The loop
		int[][] resultMatrix = new int[m][n];
		for (int i = 0; i < m; i++) {
			for(int j = 0; j < n; j++) {
				for(int k =0; k<n; k++) {
					resultMatrix[i][j] += paraMatrix1[i][k] *paraMatrix2[k][j];
				}// Of for k
			}// Of for j
		}// Of for k
		
		return resultMatrix;
	}// Of multiplication
}// Of class

运行结果：

The first matrix is: [[0, 1, 2], [1, 2, 3]]
The Second matrix is: [[0, 1, 2, 3], [2, 3, 4, 5], [4, 5, 6, 7]]
The Third matrix is: [[10, 13, 16], [16, 22, 28]]
Trying to multiply the first matrix with itself.
The two matrices cannot be multiplied.
The matrix multiply with itself is: null

public static不知何时用int，何时用void、等？