PCTuning fórum

Kód: Vybrat vše

package maticeproject2009;

final public class Matrix {
    private final int M;             // number of rows
    private final int N;             // number of columns
    private final double[][] data;   // M-by-N array

    // create M-by-N matrix of 0's
    public Matrix(int M, int N) {
        this.M = M;
        this.N = N;
        data = new double[M][N];
    }

    // create matrix based on 2d array
    public Matrix(double[][] data) {
        M = data.length;
        N = data[0].length;
        this.data = new double[M][N];
        for (int i = 0; i < M; i++)
            for (int j = 0; j < N; j++)
                    this.data[i][j] = data[i][j];
    }

    // copy constructor
    private Matrix(Matrix A) { this(A.data); }

    // print matrix to standard output
    public void show() {
        for (int i = 0; i < M; i++) {
            for (int j = 0; j < N; j++)
                System.out.printf("%9.4f ", data[i][j]);
            System.out.println();
        }
    }
    
    public Matrix gaussian() {
        // create copies of the data
        Matrix A = new Matrix(this);

        // Gaussian elimination with partial pivoting
        for (int i = 0; i < N; i++) {

            // find pivot row and swap
            int max = i;
            for (int j = i + 1; j < N; j++)
                if (Math.abs(A.data[j][i]) > Math.abs(A.data[max][i]))
                    max = j;
            A.swap(i, max);

            // pivot within A
            for (int j = i + 1; j < N; j++) {
                double m = A.data[j][i] / A.data[i][i];
                for (int k = i+1; k < N; k++) {
                    A.data[j][k] -= A.data[i][k] * m;
                }
                A.data[j][i] = 0.0;
            }
        }
        return A;
    }

    // swap rows i and j
    private void swap(int i, int j) {
        double[] temp = data[i];
        data[i] = data[j];
        data[j] = temp;
    }

    // test client
    public static void main(String[] args) {
        double[][] d = { { 8, -1, -2, 0 }, { -1, 7, -1, 10 }, { -2, -1, 9, 23} };
        Matrix A = new Matrix(d);
        A.show();
        System.out.println();

        A.gaussian();
        System.out.println("Uprava na schodovy tvar:");
        A.show();
    }
}

Kód: Vybrat vše

if (Math.abs(A.data[j][i]) > Math.abs(A.data[max][i]))

Kód: Vybrat vše

...
// find pivot row and swap
int max = i;
for (int j = i + 1; j < N; j++)
if (Math.abs(A.data[j][i]) > Math.abs(A.data[max][i]))
....

Kód: Vybrat vše

private final int M;             // number of rows

Kód: Vybrat vše

while (i ≤ m and j ≤ n) do
  Find pivot in column j, starting in row i:
  maxi := i
  for k := i+1 to m do
    if abs(A[k,j]) > abs(A[maxi,j]) then
      maxi := k
    end if