多項式計算調用庫函數pow方法和秦九韶算法,我們來測算下他們的運行效率

計算函數f(x)=1+(Σxi/i)(i從1取到m);

用ctime時間函數來測試運行時間，帶入x=0.9來計算

#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--) /*秦九韶多項式算法*/f = f*x + 1.0 / i;return f*x + 1.0;}

運行時間見下表格

從運行時間的結果可以看出來，秦九韶算法效率遠遠高于pow調用方法