原理：
例如：用牛顿法求下面方程在1.5附近的根：
2*x^3 - 4*x^2 + 3*x -6 = 0
故有：f(x) = 2*x^3 - 4*x^2 + 3*x - 6
df/dx = 6*x^2 - 8*x + 3
x := x - f(x)/(df/dx);
C代码实现：
1 #include <stdio.h> 2 #include <math.h> 3 4 5 /*****************************************NEWTON'S METHODS FOR GETTING THE ROOT OF A FUNCTION*********************************************************/ 6 7 /*function f(x)*/ 8 double f(double x) 9 { 10 return 2*pow(x,3) - 4*pow(x,2) + 3*x - 6; 11 } 12 /*function df/dx that is f'(x) */ 13 double df(double x) 14 { 15 return 6*x*x - 8*x + 3; 16 } 17 18 /*theta is the parameter of function f, and the parameter of function df*/ 19 double Newton( double theta,double (*f)(double), double (*df)(double), const double precision ) 20 { 21 22 double x1 = (*f)(theta); 23 double x2; 24 do{ 25 x2 = x1 - (*f)(x1)/(*df)(x1); 26 }while( fabs(x2-x1) < precision ? 0: (x1 = x2)); 27 return x2; 28 } 29 30 int main() 31 { 32 double (*pf)(double) = f; 33 double (*pdf)(double) = df; 34 /*test*/ 35 printf("%lf",Newton(1.5,pf,pdf,0.0001)); 36 return 0; 37 }