# How to multiply two matrices

```public class Matrix {   /* Matrix-multiply two arrays together.   * The arrays MUST be rectangular.   * @author Tom Christiansen & Nathan Torkington, Perl Cookbook version.   */   public static int[][] multiply(int[][] m1, int[][] m2) {     int m1rows = m1.length;     int m1cols = m1[0].length;     int m2rows = m2.length;     int m2cols = m2[0].length;     if (m1cols != m2rows)       throw new IllegalArgumentException("matrices don't match: " + m1cols + " != " + m2rows);     int[][] result = new int[m1rows][m2cols];     // multiply     for (int i=0; i<m1rows; i++)       for (int j=0; j<m2cols; j++)         for (int k=0; k<m1cols; k++)         result[i][j] += m1[i][k] * m2[k][j];     return result;   }   /** Matrix print.   */   public static void mprint(int[][] a) {     int rows = a.length;     int cols = a[0].length;     System.out.println("array["+rows+"]["+cols+"] = {");     for (int i=0; i<rows; i++) {       System.out.print("{");       for (int j=0; j<cols; j++)         System.out.print(" " + a[i][j] + ",");       System.out.println("},");     }     System.out.println(":;");   }   public static void main(String[] argv) {     //+     int x[][] = {       { 3, 2, 3 },       { 5, 9, 8 },     };     int y[][] = {       { 4, 7 },       { 9, 3 },       { 8, 1 },     };     int z[][] = Matrix.multiply(x, y);     Matrix.mprint(x);     Matrix.mprint(y);     Matrix.mprint(z);       } }```