How to format matrix multiplication in java

Question

So for this part of my homework, I need to do matrix multiplication and here is the general criteria:

As far as the computation goes, I had no problem doing it however, my professor says that if any double in the component is .00 it must be represented then as an integer like 24 in a(ij) = a(13) = 24 as you see in the homework example. However, in my case, no matter what I try, I cannot get it to be an integer of 24 without getting rid of the decimal format.

Furthermore, when I print out my result, I start on a new line away from the last output line: "Multiplication of the matrices is: "

Whereas the homework example shows the first row of multiplied matrix on the same line as the output and formatted perfectly for the following rows.

Someone please help. I don't know why my professor is so strict about design over function but I've been trying to figure this out for a few hours and I am stuck.

import java.text.DecimalFormat;
import java.util.Scanner;

public class ProblemFour {
    public static void main(String[] args) {
        System.out.print("Enter matrix1: ");
        Scanner stdin = new Scanner(System.in);
        String a = stdin.nextLine();
        System.out.print("Enter matrix2: ");
        String b = stdin.nextLine();
        ProblemFour o = new ProblemFour();
        double[][] matrixA = new double[3][3];
        double[][] matrixB = new double[3][3];
        String[] nums1 = a.split(" ");
        String[] nums2 = b.split(" ");
        if (nums1.length == nums2.length) {
            matrixA = o.makeMatrix(nums1);
            matrixB = o.makeMatrix(nums2);
            double[][] matrixC = o.multiplyMatrix(matrixA, matrixB);
            for (int i = 0; i < 3; i++) {
                System.out.println(" ");
                if (i == 0) {
                    System.out.println("Multiplication of the matrices is: ");
                }
                System.out.println(" ");
                for (int j = 0; j < 3; j++) {
                    System.out.print(matrixC[i][j] + " ");
                }
            }
        } else {
            System.out.println("matrix1 column not equal to matrix2 row");
            stdin.close();
        }
    }

    public double[][] makeMatrix(String[] nums) {
        double[][] matrix = new double[3][3];
        for (int i = 0; i < matrix.length; i++) {
            for (int j = 0; j < matrix[0].length; j++) {
                int n = matrix[j].length * i + j;
                matrix[i][j] = Double.parseDouble(nums[n]);
            }
        }
        return matrix;
    }

    public static double[][] multiplyMatrix(double[][] a, double[][] b) {
        double totalElem = 0.0;
        double[][] multipliedMatrix = new double[3][3];
        for (int i = 0; i < 3; i++) {
            for (int j = 0; j < 3; j++) {
                for (int k = 0; k < 3; k++) {
                    DecimalFormat df = new DecimalFormat("##.#");
                    double current = a[i][k] * b[k][j];
                    double newdf = Double.parseDouble(df.format(current));
                    totalElem += newdf;
                    if (k == 2) {
                        int roundInt = (int) totalElem;
                        if (totalElem - roundInt == 0.0) {
                            multipliedMatrix[i][j] = roundInt;
                        } else {
                            multipliedMatrix[i][j] = totalElem;
                        }
                        totalElem = 0;
                    }
                }
            }
        }
        return multipliedMatrix;
    }
}

I am guessing in order to format it how my professor wants it, I need to do it in the main class after I call on my method to multiply the matrix.. am I right? — swordlordswamplord, Mar 19 '20 at 12:17
Please try to avoid picture and send actual code in `proper tags` — Silverfang, Mar 19 '20 at 12:18
Well it will not work because you have declared your 2-d matrix as double. So if you store a int value in it It will automatically convert it into double — Silverfang, Mar 19 '20 at 12:32
Resulting in that `.0` every time so your if else condition will basically have no effect. Although I am not sure why it have to have the exact format. Well you can always do the workaround by using a string 2D array. — Silverfang, Mar 19 '20 at 12:38
yes I realized if I am to change it from double to int i need to convert it to a string in the main class. a bit annoying but whatever — swordlordswamplord, Mar 19 '20 at 18:37

score 0 · Answer 1 · answered Mar 19 '20 at 13:04

0

Let's give you clues

...
String.format("%4d",(int)elem)
...
String.format("%2.1f",elem)

also you will need this

How to test if a double is an integer

answered Mar 19 '20 at 13:04

classeswilldullyourmind

91
9

How to format matrix multiplication in java

1 Answers1