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hw_numerandbisec

#include <stdio.h>
#include <math.h>

const double ROOT3 = 1.73205080756887729352744634150587236694280525381;

double f(double x) {
	return (x*x - 3);
}

double df(double x) {
	return (2 * x);
}

int swap(double *a, double *b) {
	int tmp = *a;
	*a = *b;
	*b = tmp;
	return 0;
}

//Usage: newton(ค่าเริ่มต้น, จำนวนครั้ง, ฟังชั้น, อนุพันธ์พังชั้น);
//Return: ตำแหน่ง x ใกล้ 0
double newton(double start, int n, double fc(double x), double dfc(double x)) {
	double x = start, error;
	int sign;

	if (fc(start) > 0.0) {
		sign = -1;
	}
	else {
		sign = 1;
	}

	for (int i = 0; i <= n; i++){
		x = x + (fc(x) / dfc(x))*sign;
		error = ROOT3 - x;
		printf("x = %.16f\n", x);
		printf("log|error| = %.16f\n", log10(fabs(error)));
	}
	return x;
}

//Usage: newton(ค่าด้านซ้าย, ค่าด้านขวา, จำนวนครั้ง, ฟังชั้น);
//Return: ตำแหน่ง x ใกล้ 0
double bisection(double a, double b, int n, double fc(double x)) {
	double check, error;
	if (a > b) {
		swap(&a, &b);
	}
	for (int i = 0; i <= n; i++) {
		check = (a + b) / 2;
		if (fc(check) >= 0) {
			b = check;
		}
		else {
			a = check;
		}
		error = ROOT3 - check;
		printf("x = %.16f\n", check);
		printf("log|error| = %.16f\n", log10(fabs(error)));
	}
	return check;
}

int main(int argc, char *argv []) {
	printf("Newton Method Test\n");
	newton(3.0, 10, f, df);
	printf("\nbisection Method Test\n");
	bisection(1.0, 3.0, 10, f);
	return 0;
}