public class juzhengxiangcheng {

	 public static int[][] matrix(int a[][], int b[][]) {
	        //当a的列数与矩阵b的行数不相等时，不能进行点乘，返回null
	        if (a.length != b[0].length)
	            return null;
	        //c矩阵的行数y，与列数x
	       int N=a.length;
	        int c[][] = new int[N][N];
	        for (int i = 0; i < N; i++)
	            for (int j = 0; j < N; j++)
	                //c矩阵的第i行第j列所对应的数值，等于a矩阵的第i行分别乘以b矩阵的第j列之和
	                for (int k = 0; k < N; k++)
	                    c[i][j] += a[i][k] * b[k][j];
	        return c;
	 }
}