题目
#include<stdio.h>float lagelangri(float x[],float y[],float xx,int n){ int i,j; float *a,yy=0; a=new float[n]; for(i=0;i<=n-1;i++) { a[i]=y[i]; for(j=0;j<=n-1;j++) if(j!=i)a[i]*=(xx-x[j])/(x[i]-x[j]); yy+=a[i]; } delete a; return yy;}void main(){ float x[5]={-3.0,-1.0,1.0,2.0,3.0}; float y[5]={1.0,1.5,2.0,2.0,1.0}; float xx1=-2,xx2=0,xx3=2.75,yy1,yy2,yy3; yy1=lagelangri(x,y,xx1,3); yy2=lagelangri(x,y,xx2,3); yy3=lagelangri(x,y,xx3,3); printf("x1=%-20f,y1=%f\n",xx1,yy1); printf("x2=%-20f,y2=%f\n",xx2,yy2); printf("x3=%-20f,y3=%f\n",xx3,yy3);}
(2)五次插值:
#include<stdio.h>float lagelangri(float x[],float y[],float xx,int n){ int i,j; float *a,yy=0; a=new float[n]; for(i=0;i<=n-1;i++) { a[i]=y[i]; for(j=0;j<=n-1;j++) if(j!=i)a[i]*=(xx-x[j])/(x[i]-x[j]); yy+=a[i]; } delete a; return yy;}void main(){ float x[6]={0.30,0.42,0.50,0.58,0.66,0.72}; float y[6]={1.04403,1.08462,1.11803,1.15603,1.19817,1.23223}; float xx1=0.46,xx2=0.55,xx3=0.60,yy1,yy2,yy3; yy1=lagelangri(x,y,xx1,6); yy2=lagelangri(x,y,xx2,6); yy3=lagelangri(x,y,xx3,6); printf("x1=%-20f,y1=%f\n",xx1,yy1); printf("x2=%-20f,y2=%f\n",xx2,yy2); printf("x3=%-20f,y3=%f\n",xx3,yy3);}
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