midinf.cpp

来自「提供了6种数值积分方法的c++代码实现： 1 梯形求积法(TRAPZD->」· C++ 代码 · 共 36 行

double inf(double x)
{
    return func(1 / x) / pow(x , 2);
}

void midinf(double aa, double bb, double& s, int n)
{
    int ii,tnm,j;
	double del,ddel,x,sum;
	double b = 1.0 / aa;
    double a = 1.0 / bb;
    if (n == 1)
	{
        s = (b - a) * inf(0.5 * (a + b));
        ii = 1;
	}
    else
	{
        ii = (int)pow(3 , n - 2);
        tnm = ii;
        del = (b - a) / (3.0 * tnm);
        ddel = del + del;
        x = a + 0.5 * del;
        sum = 0.0;
        for (j = 1; j<=ii; j++)
		{
            sum = sum + inf(x);
            x = x + ddel;
            sum = sum + inf(x);
            x = x + del;
        }
        s = (s + (b - a) * sum / tnm) / 3.0;
    }
}