tixing.c

我自己写的数值分析课程设计的算法

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

#define e 2.718282
#define pi 3.1415926

double f1(double x)
{
	return (1+x*x)/(1+pow(x,4));
}
double f2(double x)
{
	return log(1+sqrt(x));
}
double f3(double x)
{
	return 1/(pow(cos(x),2)+4*pow(sin(x),2));
}
double (*ff)(double)=NULL;

void main()
{
	double a,b;
	int num;
	int m;
	int j;
	double x,xx;
	double x1=0;
	double x2=0;
	double x0=0;
	double ERR,h;
	FILE *file;

	file=fopen("tixing.txt","a+");
	printf("Enter m,a,b:\n");
	scanf("%d%Lg%Lg",&m,&a,&b);
	printf("Enter the function number:\n");
	scanf("%d",&num);

	fprintf(file,"The function is: f%d\n",num);
	fprintf(file,"From %Lg to %0.9Lg divided into %d\n",a,b,m);
	h=(b-a)/m;
	
	switch(num)
	{
	case 1:
		ff=f1;
		break;
	case 2:
		ff=f2;
		break;
	case 3:
		ff=f3;
		break;
	}

	x0=ff(a)+ff(b);
	for(j=1;j<m;j++)
	{
		x=a+h*j;
		x1+=ff(x);
	}

	xx=h*(x0+2*x1)/2;
	switch(num)
	{
	case 1:
		 ERR=xx-pi/4*sqrt(2);
		 break;
	case 2:
		 ERR=xx-0.5;
		 break;
	case 3:
		 ERR=xx-pi/4;
		 break;
	}
	
	fprintf(file,"x=%Lg\n",xx);
	fprintf(file,"ERR=%Lg\n\n",ERR);
	fclose(file);
}