A-M baby

Task/Matrix-arithmetic/C/matrix-arithmetic-1.c

@@ -0,0 +1,45 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+double det_in(double **in, int n, int perm)
+{
+	if (n == 1) return in[0][0];
+
+	double sum = 0, *m[--n];
+	for (int i = 0; i < n; i++)
+		m[i] = in[i + 1] + 1;
+
+	for (int i = 0, sgn = 1; i <= n; i++) {
+		sum += sgn * (in[i][0] * det_in(m, n, perm));
+		if (i == n) break;
+
+		m[i] = in[i] + 1;
+		if (!perm) sgn = -sgn;
+	}
+	return sum;
+}
+
+/* wrapper function */
+double det(double *in, int n, int perm)
+{
+	double *m[n];
+	for (int i = 0; i < n; i++)
+		m[i] = in + (n * i);
+
+	return det_in(m, n, perm);
+}
+
+int main(void)
+{
+	double x[] = {	0, 1, 2, 3, 4,
+			5, 6, 7, 8, 9,
+			10, 11, 12, 13, 14,
+			15, 16, 17, 18, 19,
+			20, 21, 22, 23, 24 };
+
+	printf("det:  %14.12g\n", det(x, 5, 0));
+	printf("perm: %14.12g\n", det(x, 5, 1));
+
+	return 0;
+}