Data commit

Task/Gaussian-elimination/C/gaussian-elimination.c

@@ -0,0 +1,73 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <math.h>
+
+#define mat_elem(a, y, x, n) (a + ((y) * (n) + (x)))
+
+void swap_row(double *a, double *b, int r1, int r2, int n)
+{
+	double tmp, *p1, *p2;
+	int i;
+
+	if (r1 == r2) return;
+	for (i = 0; i < n; i++) {
+		p1 = mat_elem(a, r1, i, n);
+		p2 = mat_elem(a, r2, i, n);
+		tmp = *p1, *p1 = *p2, *p2 = tmp;
+	}
+	tmp = b[r1], b[r1] = b[r2], b[r2] = tmp;
+}
+
+void gauss_eliminate(double *a, double *b, double *x, int n)
+{
+#define A(y, x) (*mat_elem(a, y, x, n))
+	int i, j, col, row, max_row,dia;
+	double max, tmp;
+
+	for (dia = 0; dia < n; dia++) {
+		max_row = dia, max = A(dia, dia);
+
+		for (row = dia + 1; row < n; row++)
+			if ((tmp = fabs(A(row, dia))) > max)
+				max_row = row, max = tmp;
+
+		swap_row(a, b, dia, max_row, n);
+
+		for (row = dia + 1; row < n; row++) {
+			tmp = A(row, dia) / A(dia, dia);
+			for (col = dia+1; col < n; col++)
+				A(row, col) -= tmp * A(dia, col);
+			A(row, dia) = 0;
+			b[row] -= tmp * b[dia];
+		}
+	}
+	for (row = n - 1; row >= 0; row--) {
+		tmp = b[row];
+		for (j = n - 1; j > row; j--)
+			tmp -= x[j] * A(row, j);
+		x[row] = tmp / A(row, row);
+	}
+#undef A
+}
+
+int main(void)
+{
+	double a[] = {
+		1.00, 0.00, 0.00,  0.00,  0.00, 0.00,
+		1.00, 0.63, 0.39,  0.25,  0.16, 0.10,
+		1.00, 1.26, 1.58,  1.98,  2.49, 3.13,
+		1.00, 1.88, 3.55,  6.70, 12.62, 23.80,
+		1.00, 2.51, 6.32, 15.88, 39.90, 100.28,
+		1.00, 3.14, 9.87, 31.01, 97.41, 306.02
+	};
+	double b[] = { -0.01, 0.61, 0.91, 0.99, 0.60, 0.02 };
+	double x[6];
+	int i;
+
+	gauss_eliminate(a, b, x, 6);
+
+	for (i = 0; i < 6; i++)
+		printf("%g\n", x[i]);
+
+	return 0;
+}