bzoj1013 [ JSOI2008 ] -- 高斯消元

 1 #include<iostream>
 2 #include<cstdio>
 3 #include<cstring>
 4 #include<cmath>
 5 using namespace std;
 6 #define N 20
 7 double a[N][N],b[N],x;
 8 int i,j,k,n,m;
 9 inline void Guass(){
10     for(int i=1;i<=n;i++){
11         double Ma=-1;int x;
12         for(int j=i;j<=n;j++)if(fabs(a[j][i])>Ma)Ma=fabs(a[j][i]),x=j;
13         if(x!=i)for(int j=1;j<=n+1;j++)swap(a[i][j],a[x][j]);
14         double t=a[i][i];
15         for(int j=1;j<=n+1;j++)a[i][j]/=t;
16         for(int j=1;j<=n;j++)
17         if(i!=j){
18             double t=a[j][i];
19             for(int k=1;k<=n+1;k++)
20             a[j][k]-=t*a[i][k];
21         }
22     }
23 }
24 int main()
25 {
26     scanf("%d",&n);
27     for(i=1;i<=n;i++)scanf("%lf",&b[i]);
28     for(i=1;i<=n;i++){
29         for(j=1;j<=n;j++)
30         scanf("%lf",&x),a[i][j]=(x-b[j])*2,a[i][n+1]+=x*x-b[j]*b[j];
31     }
32     Guass();
33     for(printf("%.3lf",a[1][n+1]),i=2;i<=n;i++)printf(" %.3lf",a[i][n+1]);
34     return 0;
35 }