多项式计算调用库函数pow方法和秦九韶算法,我们来测算下他们的运行效率

计算函数f(x)=1+(Σxi/i)(i从1取到m);

用ctime时间函数来测试运行时间，带入x=0.9来计算

#include<iostream>#include<cmath>;#include<ctime>using namespace std;double Fn1(double x);double Fn2(double x);#define m 1000000000clock_t start, stop;int main(){double x;x = 0.9;start = clock();cout << Fn1(x) << endl;stop = clock();cout << double(stop - start) / CLK_TCK << endl;//-----------------------------------start = clock();cout << Fn2(x) << endl;stop = clock();cout << double(stop - start) / CLK_TCK << endl;return 0;}double Fn1(double x){int i;double f=1.0;for (i = 1; i <= m; i++)f += pow(x, i)/i;return f;}double Fn2(double x){int i;double f = 0.0;for (i = m; i >= 1; i--) /*秦九韶多项式算法*/f = f*x + 1.0 / i;return f*x + 1.0;}

运行时间见下表格

从运行时间的结果可以看出来，秦九韶算法效率远远高于pow调用方法