NumericalMethods/lab10/lab10.c

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

#define A -3
#define B 3
double Func(double x){
	return x*x*x*x*x - 5.2*x*x*x + 5.5*x*x - 7*x; 
}

double ModifiedFunc(double x){
	return x*x*x*x*x - 5.2 * fabs(x*x*x) + 5.5*x*x - 7*x; 
}

double trapezoidalIntegral(int n, double previousResult, double (*func)(double x)) {
	double result = 0.0;
	double h;
	int i;

	h = (B - A) / (double)n;     //Разобьем отрезок [a, b] на N интервалов длиной h
	if (n == 1){
		result = (func(A) + func(B)) * h / 2;
	    for (i = 1; i < n; i++) {
		    result += func(A + i * h) * h;
	    }		
	}else{
		result = previousResult/2.0;       //Использовать результат n/2 
        for (i = 1; i < n; i += 2) {
            result += func(A + i * h) *h; 
        }
    }	
	return result;
}

double Integral(double eps, int *k, int *n, double (*func)(double x)){
	(*n) = 1;
	double next= trapezoidalIntegral(*n, 0, func);
	double prev;
	(*k) = 0;
	
	do{
		(*n) = (*n)*2;
		prev = next;
		next = trapezoidalIntegral(*n, prev, func);
		(*k) = (*k)+1;
	} while (fabs(next - prev)/3 >= eps);
	
	return next;
}

int main(){
	FILE *f = fopen("data.txt", "w");
    if (f == NULL) {
        printf("Error opening file!\n");
        return 1;
    }
    
    int i, k, n;
    double Iexact = 99.0;
    double eps = 0.1;
    double result;

    for(i = 0; i<9; i++){
    	result = Integral(eps, &k, &n, Func);
    	fprintf(f, "%.15f %d %.15f \n", fabs(Iexact-result), k, log2((double)(B-A)/n));  
		eps = eps/10;  
	}
    
    fclose(f);
    return 0;    
}