Multiplying Matrixes
Problem
You need to multiply a pair of two-dimensional arrays, as is common in mathematical and engineering applications.
Solution
Use the following code as a model.
Discussion
It is straightforward to multiply an array of a numeric type. The code in Example 5-3 implements matrix multiplication.
Example 5-3. Matrix.java
/** * Multiply two matrices. * Only defined for int: clone the code (or wait for Templates) * for long, float, and double. */ 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( 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; } 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(":;"); } }
Here is a program that uses the
Matrix
class to multiply two arrays of
int
s:
// MatrixUse.java int x[][] = { { 3, 2, 3 }, { 5, 9, 8 }, }; ...
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