I'm trying to write a method that multiplies two matrices together and returns a 2D array with the resulting product. For example, the first matrix is a 5 x 2, and the second is a 2 x 5. The resulting matrix should be a 5 x 5 matrix respectively.
This is what I have so far:
public static int[][] multiplyArrays(int[][] arrayA, int[][] arrayB) {
int[][] arrayProduct = new int[arrayA.length][arrayB[0].length];
for (int cRow = 0; cRow < arrayA.length; cRow++) {
for (int dCol = 0; dCol < arrayB[0].length; dCol++) {
for (int i = 0; i < arrayB[0].length; i++) {
arrayProduct[cRow][dCol] += arrayA[cRow][i] * arrayB[i][dCol];
}
}
}
}
Whenever I'm runnning this code, it keeps giving me an exception saying ArrayIndexOutOfBoundsException: 2?
What is wrong with my logic in the code?
Any help is greatly appreciated!
EDIT: The fixed version of this code would be
public static int[][] multiplyArrays(int[][] arrayA, int[][] arrayB) {
int[][] arrayProduct = new int[arrayA.length][arrayB[0].length];
for (int cRow = 0; cRow < arrayA.length; cRow++) {
for (int dCol = 0; dCol < arrayB[0].length; dCol++) {
for (int i = 0; i < arrayA[0].length; i++) {**
arrayProduct[cRow][dCol] += arrayA[cRow][i] * arrayB[i][dCol];
}
}
}
}
In the inner-most loop use
for (int i = 0; i < arrayA[0].length; i++)
instead of
for (int i = 0; i < arrayB[0].length; i++)
Related
Create a basics.Matrix class (using a two-dimensional array of real numbers as a matrix) that has the following operations: construct an M × N zero matrix, construct an M × N matrix using an M × N array, create an N × N dimensional unit matrix ( the result matrix should be a return value), the matrix transposed resp. calculating the sum and difference of two matrices, representing the matrix as a string (use java.lang.StringBuilder to generate the text).
Also create a main program (Main.java) that tests these operations!
My problem is in my basicsMatrixMain.java code, that I do not know how can I print out thre results I get from difference or transpone. Can anybody help me to solve it ?
public class basicsMatrix {
private final int N;
private final int M;
private final double[][] matrix;
public basicsMatrix(int M, int N) {
this.N = N;
this.M = M;
matrix = new double[M][N];
}
public basicsMatrix(double[][] matrix) {
M = matrix.length;
N = matrix[0].length;
this.matrix = new double[N][M];
for (int i = 0; i < M; i++)
for (int j = 0; j < N; j++)
this.matrix[i][j] = matrix[i][j];
}
public void transzponalas(double[][] matrix1){
double[][] transpose = new double[M][N];
for(int i = 0; i < N; i++) {
for (int j = 0; j < M; j++) {
transpose[j][i] = matrix1[i][j];
}
}
}
public void add(double[][] matrix1,double[][] matrix2){
double[][] osszeadas = new double[N][M];
for(int i = 0; i < N; i++) {
for (int j = 0; j < M; j++) {
osszeadas[i][j] = (matrix1[i][j] + matrix2[i][j]);
}
}
}
public void difference(int matrix1[][], int matrix2[][]){
double[][] kivonas = new double[N][M];
for(int i = 0; i <= N; i++){
for(int j = 0; j <= M; j++){
kivonas[i][j] = matrix1[i][j] - matrix2[i][j];
}
}
}
public String matrixtostring(double[][] matrix1){
StringBuilder sb = new StringBuilder();
for (int i = 0; i < N; i++) {
for (int j = 0; j < M; j++) {
sb.append(matrix1);
}
}
return sb.toString();
}
}
public class basicsMatrixMain {
public static void main(String[] args) {
int N = 2;
int M = 3;
double[][] matrix1 = { {2, 3, 4}, {5, 2, 3} };
double[][] matrix2 = { {-4, 5, 3}, {5, 6, 3} };
System.out.println("\n");
System.out.print("Difference:");
for(int i = 0; i <= N; i++){
for(int j = 0; j <= M; j++){
System.out.println();
}
}
}
}
You have defined a lot of functions in basicsMatrix that you can use here.
However there are some changes that you need to make. In your add, difference and transpose methods, you define something but you never save the result. I would recommend something like this:
public double[][] transzponalas(double[][] matrix1){
double[][] transpose = new double[M][N];
for(int i = 0; i < N; i++) {
for (int j = 0; j < M; j++) {
transpose[j][i] = matrix1[i][j];
}
}
return transpose;
}
public double[][] add(double[][] matrix1,double[][] matrix2){
double[][] osszeadas = new double[N][M];
for(int i = 0; i < N; i++) {
for (int j = 0; j < M; j++) {
osszeadas[i][j] = (matrix1[i][j] + matrix2[i][j]);
}
}
return osszeadas;
}
public double[][] difference(int matrix1[][], int matrix2[][]){
double[][] kivonas = new double[N][M];
for(int i = 0; i <= N; i++){
for(int j = 0; j <= M; j++){
kivonas[i][j] = matrix1[i][j] - matrix2[i][j];
}
}
return kivonas;
}
All these functions now return a matrix that you can print out.
Now you just print you matrices. Something like this should work.
System.out.println(matrixtostring(transzponalas(matrix1)));
System.out.println(matrixtostring(add(matrix1,matrix2)));
System.out.println(matrixtostring(difference(matrix1,matrix2)));
Looking at the question description.
"Create a basics.Matrix class (using a two-dimensional array of real numbers as a matrix) that has the following operations: construct an M × N zero matrix, construct an M × N matrix using an M × N array, create an N × N dimensional unit matrix ( the result matrix should be a return value), the matrix transposed resp. calculating the sum and difference of two matrices, representing the matrix as a string (use java.lang.StringBuilder to generate the text).
Also create a main program (Main.java) that tests these operations!"
I suspect that you are supposed to create a class that calls functions on itself. In other words the basicsMatrix will become your matrix.
For example, the transzponalas method would become
public void transzponalas(){
double[][] transpose = new double[M][N];
for(int i = 0; i < N; i++) {
for (int j = 0; j < M; j++) {
transpose[j][i] = this.matrix[i][j];
}
}
int tmp = this.M
this.M = this.N
this.N = tmp
this.matrix = transpose;
}
This way, you change the matrix that is inside your basicsMatrix. You should make sure that you understand the assignment correctly.
I searched some entries, but could not answer my question correctly myself.
I'm trying to fill a 2-dimensional array with values.
As a test I'm currently doing this by trying to fill the array with the int number 1.
I do not understand my mistake.
public static void creatBoard () {
final int L = 6;
final int H = 6;
// Modell:
int [] [] board = new int [L] [H];
for (int i = 0; i<=board.length; i++) {
for (int j = 0; j<=board.length; j++) {
board [i] [j] = 1;
}
System.out.println("");
}
Use index 0 to length-1 (as array index start with 0)
public static void creatBoard () {
final int L = 6;
final int H = 6;
// Modell:
int [] [] board = new int [L] [H];
for (int i = 0; i<board.length; i++) {
for (int j = 0; j<board[i].length; j++) {
board [i] [j] = 1;
}
System.out.println("");
}
}
just debug it and you can see, that
for (int i = 0; i<=board.length; i++) {
for (int j = 0; j<=board.length; j++) {
board [i] [j] = 1;
}
System.out.println("");
}
i, and j change values from 0 to 6, it means that it get's out of arrays bounds ( you iterate over 7 lements, instead of 6 ), just remove = sign in loop bodies
for (int i = 0; i<board.length; i++) {
for (int j = 0; j<board[i].length; j++) {
board [i] [j] = 1;
}
System.out.println("");
}
Your board array is of size 6x6 hence the board.length is 6.
When you run the loop for (int j = 0; j<=board.length; ij+) it will run from 0 up to 6 but the array indexing is from 0 to 5. So when j=6, ExceptionOutOfBounds occurs since it will be referring to index board[0][6].
Change the condition in both the loops from <=board.length to <board.length
I want to create an 8x8 array with JAVA, in which i want to have 1 eight times in random generated positions. All the other positions of the array are going to be 0. I am using this code but obviously it is not filling the array with 1 for a specific number of times.
public static void main(String[] args) {
int [][] arr = new int [8][8];
for(int i = 0; i < 8; i++){
for(int j = 0; j < 8; j++){
arr[i][j] = (int) (Math.random()*2);
}
}
for(int k = 0; k < 8; k++){
for(int l = 0; l < 8; l++){
System.out.print(arr[k][l] + " ");
}
System.out.println();
}
}
}
import java.util.Random;
int[][] array = new int[8][8];
Random r = new Random();
int a = r.nextInt(8);
int b = r.nextInt(8);
//insert 8 random 1's in the 8x8 matrix, no duplicates
//by default in Java the other places are
for(int i = 0; i < 8; i++){
while(array[a][b] == 1){
a = r.nextInt(8);
b = r.nextInt(8);
}
array[a][b] = 1;
}
public static int[][] shift(final int[][] original, final int amount) {
int[][] shifted = new int[original.length][original[0].length];
for (int col = 0; col < original.length; col++) {
for (int row = 0; row < original[col].length; row++) {
shifted[col][row] = FILL_VALUE;
}
for (int cols = 0; cols < original.length + amount; cols++) {
for (int rows = 0; rows < original[cols].length; rows++) {
if (cols - amount < original.length) {
shifted[cols][rows] = original[cols - amount][rows];
}
}
}
}
return shifted;
}
Hi,
I am trying to write a method that will shift the elements in my 2-D array to the left by some arbitrary amount. I don't want to loop the values back around, but instead fill the empty arrays with some fill_value which is already predefined. And if the shift amount is more than the orignial length, I would just return an image with only fill_value. However, this function is throwing an arrayindexoutofbound Error. But I can't think of how I should change my for loop to fix the error. Any help is appreciated! Thank you!
I believe it's because in your second outer for loop, the condition is cols < length + amount, so it will continue past the edge of the array if amount > 0. You could step through your code with a debugger and see exactly where it's going out of bounds.
The error is occurring because of following line:
shifted[cols][rows] = original[cols - amount][rows];
When cols=0, rows=0, amount=2 (say), it is trying to access original[-2][0] which does not exist.
Instead you may use following:
public class overflow1 {
static int a[][] = {{1,2,3,4,5,6},{2,3,4,5,6,7},{3,4,5,6,7,8}, {4,5,6,7,8,9}, {5,6,7,8,9,10}, {6,7,8,9,10,11}};
static int b[][] ;
static int FILL_VALUE =0;
public static int[][] shift(final int[][] original, final int amount) {
int[][] shifted = new int[original.length][original[0].length];
for (int col = 0; col < original.length; col++) {
for (int row = 0; row < original[col].length; row++) {
shifted[col][row] = FILL_VALUE;
}
for (int cols = 0; cols < original.length ; cols++) {
for (int rows = 0; rows < original[cols].length; rows++) {
if (cols - amount >=0) {
shifted[cols][rows] = original[cols - amount][rows];
}
}
}
}
return shifted;
}
public static void main(String[] arggs) {
b=shift(a,2);
System.out.println("Original array:");
for(int i=0; i<a.length; i++){
for (int j=0; j<a[i].length; j++){
System.out.print(a[i][j]+ ":");
}
System.out.println();
}
System.out.println("After shift by 2 array:");
for(int i=0; i<b.length; i++){
for (int j=0; j<b[i].length; j++){
System.out.print(b[i][j]+ ":");
}
System.out.println();
}
}
}
Here is the output for the sample:
Original array:
1:2:3:4:5:6:
2:3:4:5:6:7:
3:4:5:6:7:8:
4:5:6:7:8:9:
5:6:7:8:9:10:
6:7:8:9:10:11:
After shift by 2, array:
0:0:0:0:0:0:
0:0:0:0:0:0:
1:2:3:4:5:6:
2:3:4:5:6:7:
3:4:5:6:7:8:
4:5:6:7:8:9:
How would i transfer a 2d array into a 1d array in java. I have the code for the 2d array but dont know where to start.
The output of the 2d array is a 8 by 10 grid with the numbers going from 1-80.
public class move
{
public static void main (String[] args)
{
int[][] twoarray = new int[8][10];
int i ;
int j ;
for(i =0; i < 8; i++)
{
for(j = 0; j < 10; j++)
twoarray[i][j] = (i * 10 + j+1);
}
for(i = 0; i < 8; i++)
{
for(j = 0; j < 10; j++)
{
System.out.print(twoarray[i][j]);
System.out.print(" ");
}
System.out.println();
}
int[] array = new int[80];
}
}
Using Java 8
int[] array = Stream.of(twoarray)
.flatMapToInt(IntStream::of)
.toArray();
Using Java 7 or older
int[] array = new int[80];
int index = 0;
for (int[] row : twoarray) {
for (int val : row)
array[index++] = val;
}
You can do in your for loop:
int[] array = new int[80];
int k=0;
for(i = 0; i < 8; i++){
for(j = 0; j < 10; j++){
array[k++]=twoarray[i][j];
}
}