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53 lines
1.3 KiB
Java
53 lines
1.3 KiB
Java
public class Gauss {
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public static double[] gauss(double[][] a, double[] b) {
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int n = a.length;
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for (int row = 0; row < n; row++) {
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int best = row;
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for (int i = row + 1; i < n; i++)
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if (Math.abs(a[best][row]) < Math.abs(a[i][row]))
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best = i;
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double[] tt = a[row];
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a[row] = a[best];
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a[best] = tt;
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double t = b[row];
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b[row] = b[best];
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b[best] = t;
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for (int i = row + 1; i < n; i++)
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a[row][i] /= a[row][row];
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b[row] /= a[row][row];
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// a[row][row] = 1;
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for (int i = 0; i < n; i++) {
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double x = a[i][row];
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if (i != row && x != 0) {
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// row + 1 instead of row is an optimization
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for (int j = row + 1; j < n; j++)
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a[i][j] -= a[row][j] * x;
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b[i] -= b[row] * x;
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}
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}
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}
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return b;
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}
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// Usage example
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public static void main(String[] args) {
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double[][] a = { { 4, 2, -1 }, { 2, 4, 3 }, { -1, 3, 5 } };
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double[] b = { 1, 0, 0 };
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double[][] a1 = a.clone();
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for (int i = 0; i < a.length; i++)
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a1[i] = a[i].clone();
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double[] b1 = b.clone();
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double[] x = gauss(a, b);
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for (int i = 0; i < a.length; i++) {
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double y = 0;
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for (int j = 0; j < a[i].length; j++)
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y += a1[i][j] * x[j];
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if (Math.abs(b1[i] - y) > 1e-9) {
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System.err.println("error");
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return;
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}
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}
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}
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}
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