Thread: matrix task in java

Hello.

I have a inverse matrix task.Teacher said us that we have to create little a program which is finds inverse of the matrix which is given in code.
I did something like this and when I gave him this task he said me that "I want the program calculate itself matrix size.You wont give size of matrix like int[4][4]; this.You just will write the matrix in your code and the program will change as depend to size and calculate automatically as the matrix."

I some more explain for all of you understand more.
Example I write in code
3x3 a matrix okay.Below an example.

3 4 6
1 5 7
1 3 7

This is 3x3 matrix so its calculating.And I want now 4x4 matrix.

4 5 1 6
1 4 5 6
2 4 5 5
1 2 4 7

Also this matrix will calculate as automatically depend to matrix size.

I musnt write [4][4] or [3][3].Instead this I need to write something like will change as matrix size automatically.I hope you understand.Because Im really bored with this.Its just second month in programming for us and I have no idea about this task anymore.

Please help me.

import java.util.Scanner;
public class inversematrix {
public static void main(String[] args)
{
int[][] matrix = new int[4][4];
Scanner inputUser = new Scanner(System.in);
System.out.println("Write matrix number");
for(int row=0; row<4; row++)
{
for(int column=0; column<4; column++)
{
System.out.print("A"+(row+1)+(column+1)+" = ");
matrix[row][column] = inputUser.nextInt();
}
}
 
System.out.println("4 on 4 matris");
for(int row=0; row<3; row++)
{
for(int column=0; column<3; column++)
{
System.out.printf("%3d",matrix[row][column]);
}
System.out.print("\n");
}
 
System.out.println("Inverse of matrix calculating");
int matrixInvers[][] = {{matrix[1][1]*matrix[2][2]-matrix[1][2]*matrix[2][1],matrix[0][2]*matrix[2][1]-matrix[0][1]*matrix[2][2],matrix[0][1]*matrix[1][2]-matrix[0][2]*matrix[1][1]},
{matrix[1][2]*matrix[2][0]-matrix[1][0]*matrix[2][2],matrix[0][0]*matrix[2][2]-matrix[0][2]*matrix[2][0],matrix[0][2]*matrix[1][0]-matrix[0][0]*matrix[1][2]},
{matrix[1][0]*matrix[2][1]-matrix[1][1]*matrix[2][0],matrix[0][2]*matrix[2][0]-matrix[0][0]*matrix[2][1],matrix[0][0]*matrix[1][1]-matrix[0][1]*matrix[1][0]}};
 
System.out.println("Inverse matrix");
for(int row=0; row<3; row++)
{
for(int column=0; column<3; column++)
{
System.out.printf("%3d",matrixInvers[row][column]);
}
System.out.print("\n");
}
}
}

Originally Posted by Norm

Please edit your post and wrap your code with code tags:
[code=java]
<YOUR CODE HERE>
[/code]
to get highlighting and preserve formatting.

Define the size of the array using the value in a variable instead of hardcoding 3 or 4:

int theSize = <GET a value somewhere>;
...
int[] anArray = new int[theSize];

Use the array's .length attribute to get the size of the array.

Okay I edited my post.So

int theSize = <inputUser>;
... // this part is what I didnt get
int[] anArray = new int[theSize];

will be like this?

Could you explain some more ?

Originally Posted by Norm

Please edit the code in the post and give it proper formatting. Nested statements should be indented 3-4 spaces. All statements should NOT start in the first column.

int[] anArray = new int[theSize]; // define int array with theSize number of elements

Did you try putting that code in the program to see if it worked?

I puted your code but I got error cause of I did something wrong I think.

You said " define int array with thesize number of elements" but already I want the size is will be depend to that matrix which is will given.

Or you mean like this

import java.util.Scanner;
public class inversematrix {
public static void main(String[] args)
{
Scanner inputUser = new Scanner(System.in);
int theSize;
int theSize = <inputUser>;
...
int[] anArray = new int[theSize];
System.out.println("Write matrix number");

I thank you for your helps but Im really raw in programming yet.Please dont get mad

Originally Posted by Norm

Please copy the full text of the error messages and paste it here.

The code I posted was meant as an example. It was not supposed to be copied directly into your code.

In my sample code, set the variable: theSize to the value that was given.

When posting code be sure to wrap your code with code tags:
[code=java]
<YOUR CODE HERE>
[/code]
to get highlighting and preserve formatting.

Code and explains are below.

int theSize = <inputUser>;   
*/
Multiple markers at this line
	- Syntax error on token(s), misplaced 
	 construct(s)
	- Syntax error on token "<", delete this 
	 token
	- Duplicate local variable theSize
	- Syntax error on tokens, delete these 
	 tokens
*/
... 
int[] anArray = new int[theSize];  /// anArray can not be resolved to a variable
 
System.out.println("Write matrix number");

Originally Posted by Norm

I can't tell what the full code is from what you posted. When I put these two lines in a method and compile it, there are no errors:

      int theSize = 3;
      int[] anArray = new int[theSize];

Make a small, complete class file that compiles and shows the error and post it.

I begin to understand somethings there is written "anArray" is not an Array.I wrote [] too but dont know why.Code and error below.

import java.util.Scanner;
public class inversematrix{
public static void main(String[] args)
{
Scanner inputUser = new Scanner(System.in);
int theSize = 3;
int[] anArray = new int[theSize];
System.out.println("Write matrix number");
   for(int row=0; row<4; row++)
{
   for(int column=0; column<4; column++)
{
   System.out.print("A"+(row+1)+(column+1)+" = ");
anArray[row][column] = inputUser.nextInt();  // The type of the expression must be an array type but it resolved to int

And rest of code is like I wrote in first message.Also another parts have error too but I think if we can solve this part then I can finish rest of task by myself.

Okay here the full code.

import java.util.Scanner;
public class keke {
public static void main(String[] args)
{
Scanner inputUser = new Scanner(System.in);
int theSize = 3;
int[] anArray = new int[theSize];
System.out.println("Write matrix number");
   for(int row=0; row<4; row++)
{
   for(int column=0; column<4; column++)
{
   System.out.print("A"+(row+1)+(column+1)+" = ");
anArray[row][column] = inputUser.nextInt();
}
}
 
System.out.println("4 na 4 matris");
   for(int row=0; row<3; row++)
{
   for(int column=0; column<3; column++)
{
   System.out.printf("%3d",matrix[row][column]);
}
System.out.print("\n");
}
 
System.out.println("Inverse of matrix calculating");
int [][] = {{matrix[1][1]*matrix[2][2]-matrix[1][2]*matrix[2][1],matrix[0][2]*matrix[2][1]-matrix[0][1]*matrix[2][2],matrix[0][1]*matrix[1][2]-matrix[0][2]*matrix[1][1]},
{matrix[1][2]*matrix[2][0]-matrix[1][0]*matrix[2][2],matrix[0][0]*matrix[2][2]-matrix[0][2]*matrix[2][0],matrix[0][2]*matrix[1][0]-matrix[0][0]*matrix[1][2]},
{matrix[1][0]*matrix[2][1]-matrix[1][1]*matrix[2][0],matrix[0][2]*matrix[2][0]-matrix[0][0]*matrix[2][1],matrix[0][0]*matrix[1][1]-matrix[0][1]*matrix[1][0]}};
 
System.out.println("Inverse matrix");
   for(int row=0; row<3; row++)
{
   for(int column=0; column<3; column++)
{
   System.out.printf("%3d",matrixInvers[row][column]);
}
System.out.print("\n");
}
}
}

And now at line 14 error is

Multiple markers at this line
- Line breakpoint:keke [line: 14] - main(String[])
- The type of the expression must be an array type but it

At line 23 error is

matrix cannot be resolved to a variable

At line 29 error is

Multiple markers at this line
- Syntax error on token "]", VariableDeclaratorId expected after
this token
- matrix cannot be resolved to a variable
- matrix cannot be resolved to a variable
... continues the same error matrix cannot be resolved a variable

At line 30 error is

Multiple markers at this line
- matrix cannot be resolved to a
variable
- matrix cannot be resolved to a
variable
.... going on same error like on 29.error

At line 31 the error is same with 30.

And at 38 error is

"matrixInvers cannot be resolved to a variable"

I know I made you sick but Im really trying to learn myself.Our teacher doesnt come to lesson often therefore Im trying to learn by myself in internet with helps of videos,e-books and another materials.

I really appreciate what you doing.When I will know Java well then I will help somebodies like you doing

Here I did like u wrote

anArray[row][column] = inputUser.nextInt();

But it doesnt work.

On this 14. line there is error as

Multiple markers at this line
- Line breakpoint:keke [line: 14] - main(String[])
- The type of the expression must be an array type but it

But already above of the code I definited it as int.

Decompiler error all is this

Exception in thread "main" java.lang.Error: Unresolved compilation problems:
The type of the expression must be an array type but it resolved to int
matrix cannot be resolved to a variable
Duplicate local variable anArray
matrix cannot be resolved to a variable
matrix cannot be resolved to a variable
matrix cannot be resolved to a variable
matrix cannot be resolved to a variable
matrix cannot be resolved to a variable
matrix cannot be resolved to a variable
matrix cannot be resolved to a variable
matrix cannot be resolved to a variable
matrix cannot be resolved to a variable
matrix cannot be resolved to a variable
matrix cannot be resolved to a variable
matrix cannot be resolved to a variable
matrix cannot be resolved to a variable
matrix cannot be resolved to a variable
matrix cannot be resolved to a variable
matrix cannot be resolved to a variable
matrix cannot be resolved to a variable
matrix cannot be resolved to a variable
matrix cannot be resolved to a variable
matrix cannot be resolved to a variable
matrix cannot be resolved to a variable
matrix cannot be resolved to a variable
matrix cannot be resolved to a variable
matrix cannot be resolved to a variable
matrix cannot be resolved to a variable
matrix cannot be resolved to a variable
matrix cannot be resolved to a variable
matrix cannot be resolved to a variable
matrix cannot be resolved to a variable
matrix cannot be resolved to a variable
matrix cannot be resolved to a variable
matrix cannot be resolved to a variable
matrix cannot be resolved to a variable
matrix cannot be resolved to a variable
matrix cannot be resolved to a variable
matrix cannot be resolved to a variable

at keke.main(keke.java:14)

Norm thank u too much problem has been solved.