lagrange.h

拉格朗日 计算方程的根 基本很准确 不过方法不是太通用的

#define EPS 0.000001
double lagrange(int n,double x[],double y[],double xx)
{
double p,result;
int i,j;
result = 0.0;
for(i=0;i<n;++i)
{
p=1.0;
for(j=0;j<n;++j){
if(i==j) continue;
p=p*(xx-x[j])/(x[i]-x[j]);
}
result+=(p*y[i]);
}
return(result);
} 

double device(int n,double x[],double y[],double xx){
int i;
for (i = 0; i < n; i++)
{
if (x[i] <= xx && x[i + 1] >= xx)
{
printf("\n分段线性插值公式一%f",((x[i+1]-xx)*y[i]+(xx-x[i])*y[i+1])/(x[i+1]-x[i]));
printf("\n分段线性插值公式二%f",((x[i+1]-xx)/(x[i+1]-x[i]))*y[i]+((xx-x[i])/(x[i+1]-x[i]))*y[i+1]);
//printf("\nd%d=%f",i,(y[i] * x[i] + y[i + 1] * x[i + 1]) / (x[i] + x[i + 1]));
break;
}
} 
}