算法系列-----矩阵（四）-------------矩阵的乘法

	/**
	 * 矩阵乘数的函数
	 * 
	 * @param args
	 *            参数a是个浮点型（double）的一维数组，b是浮点数；
	 * @return 返回值是一个浮点型一维数组（列向量a乘以数b的结果）
	 */
	public static double[] multi(double[] a, double b) {
		int hang = a.length;
		double[] result = new double[hang];
		for (int i = 0; i < hang; i++) {
			result[i] = a[i] * b;
		}
		return result;
	}

	/**
	 * 行向量乘以列向量的函数
	 * 
	 * @param args
	 *            参数a，b是两个浮点型（double）的一维数组
	 * @return 返回值是一个浮点型数值
	 */
	public static double multi_data(double[] a, double[] b) {
		int lie = a.length;
		double result = 0;
		for (int i = 0; i < lie; i++) {
			result += a[i] * b[i];

		}
		return result;
	}

</pre><pre name="code" class="java">	/**
	 * 列向量乘以行向量的函数
	 * 
	 * @param args
	 *            参数a，b是两个浮点型（double）的一维数组
	 * @return 返回值是一个浮点型二维矩阵
	 */
	public static double[][] multi_mat(double[] a, double[] b) {
		int hang = a.length;
		int lie = b.length;
		double[][] result = new double[hang][lie];
		for (int i = 0; i < hang; i++) {
			for (int j = 0; j < lie; j++) {
				result[i][j] = a[i] * b[j];
			}
		}
		return result;
	}

	/**
	 * 矩阵相乘的函数
	 * 
	 * @param args
	 *            参数a，b是两个浮点型（double）的二维数组
	 * @return 返回值是一个浮点型二维数组（矩阵的乘积）
	 */
	public static double[][] multi(double[][] a, double[][] b) {
		int hang = a.length;
		int lie = b[0].length;
		double sum;
		double[][] result = new double[hang][lie];
		for (int i = 0; i < hang; i++) {
			for (int j = 0; j < lie; j++) {
				sum = 0;
				for (int k = 0; k < b.length; k++) {
					sum += a[i][k] * b[k][j];
				}
				result[i][j] = sum;
			}
		}
		return result;
	}

	/**
	 * 矩阵相乘的函数
	 * 
	 * @param args
	 *            参数a是个浮点型（double）的二维数组，a是一维数组
	 * @return 返回值是一个浮点型二维数组（矩阵的乘积）
	 */
	public static double[] multi(double[][] a, double[] b) {
		int hang = a.length;

		double sum;
		double[] result = new double[hang];
		for (int i = 0; i < hang; i++) {
			sum = 0;
			for (int k = 0; k < b.length; k++) {
				sum += a[i][k] * b[k];
			}
			result[i] = sum;
		}

		return result;
	}

</pre><pre name="code" class="java">	public static void main(String[] args) {
		double[] a = { 3, 2, 1, 4};
		double[] b = { 5, 6, 9, 8};
		double[] c = {1,2};	
		
		double[][] d_a = new double[][]{{1,2},{3,4}};
		double[][] d_b = new double[][]{{7, 8}, {6, 5}};
		double[][] d_c = new double[][]{{7, 8}, {6, 5},{2,4}};
		double[][] d_testa = multi(d_a,3);
		double[][] d_testb = zjz_qh(d_b,1);
		double[][] d_testc = zjz(d_c,0,0);
		double[] s_test = multi(d_c,c);
		double result = multi_data(a,b);
		double[][] result2 = multi_mat(a,b);
		System.out.println("乘数矩阵");
		System.out.println("--------------------------------");
		print(d_testa);
		System.out.println("行向量乘以列向量");
		System.out.println("--------------------------------");
		System.out.println(result);

		System.out.println("列向量乘以行向量");
		System.out.println("--------------------------------");
		print(result2);
		System.out.println("二维矩阵和一维矩阵相乘");
		System.out.println("--------------------------------");
		print_array(s_test);
	}