midsql.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 38 行

double sql(double x, double aa)
{
    return 2 * x * func(aa + pow(x , 2));
}


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