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Thread: Matrix Inverse
 11292010, 10:00 PM #1Member
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Matrix Inverse
Hey everybody I am new to Java and to this forum. I really need help on a problem in a Java code. Any help would be really appreciated. The problem is to :
Write a test program that prompts the user to enter a11, a12, a13, a21, a22, a23, a31, a32, a33 for a matrix and displays its inverse matrix. Here is the sample runs:
Enter a11, a12, a13, a21, a22, a23, a31, a32, a33: 1 2 1 2 3 1 4 5 3
2 0.5 0.5
1 0.5 0.5
1 1.5 0.5
I never even heard of a inverse matrix but i have been doing some simple Java problem but this one is killing me please help me!
This is what i got so far:
import java.util.Scanner;
public class MatrixProblem {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
System.out.print("Enter a11, a12, a13, a21, a22, a23, a31, a32, a33: ");
double[][] A = new double[3][3];
for (int i = 0; i < 3; i++)
for (int j = 0; j < 3; j++)
A[i][j] = input.nextDouble();
double[][] inverseOfA = inverse(A);
printMatrix(inverseOfA);
}
public static void printMatrix(double[][] m) {
// ????
}
public static double[][] inverse(double[][] A) {
double[][] result = new double[A.length][A.length];
// Compute A
double determinantOfA = 1; // A[0][0] * A[1][1] * A[2][2] * ...;
result[0][0] = (A[1][1] * A[2][2]  A[1][2] * A[2][1]) / determinantOfA;
result[0][1] = 1; // ??
result[0][2] = 1; // ??
result[1][0] = 1; // ??
return result;
}
}
 11292010, 10:37 PM #2
I wouldn't recommend this for a beginner, in all honesty.
In order to find the determinant, you will need a loop. Your code currently only checks for a 2x2 matrix. Have you studied for loops at all?
 11292010, 11:19 PM #3Member
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Hey thanks for the advice but yes I have studied loops and I really do need help on this problem still. Thanks
 11292010, 11:30 PM #4Member
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Can anybody just fill in the blanks and explain what you did please. Also i did some research and I found a Java code that might help to find the inverse/determinant. So this code should help and I believe needs to be in my original code to :
public double determinant(double[][] mat) {
double result = 0;
if(mat.length == 1) {
result = mat[0][0];
return result;
}
if(mat.length == 2) {
result = mat[0][0] * mat[1][1]  mat[0][1] * mat[1][0];
return result;
}
for(int i = 0; i < mat[0].length; i++) {
double temp[][] = new double[mat.length  1][mat[0].length  1];
for(int j = 1; j < mat.length; j++) {
for(int k = 0; k < mat[0].length; k++) {
if(k < i) {
temp[j  1][k] = mat[j][k];
} else if(k > i) {
temp[j  1][k  1] = mat[j][k];
}
}
}
result += mat[0][i] * Math.pow(1, (double)i) * determinant(temp);
}
return result;
}
 12012010, 12:59 AM #5
...I really don't want to sound like this, but I can't find a better way to say it.
Are you just copying code from other places and trying to Frankenstein a program? (Or rather, trying to get us to Frankenstein it?)
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