bzoj1013 [JSOI2008]球形空间产生器sphere

题目链接

第一次写高斯消元

注意考虑分母、分子为零的情况

#include<algorithm>
#include<iostream>
#include<cstdlib>
#include<cstring>
#include<cstdio>
#include<string>
#include<cmath>
#include<ctime>
#include<queue>
#include<stack>
#include<map>
#include<set>
#define rre(i,r,l) for(int i=(r);i>=(l);i--)
#define re(i,l,r) for(int i=(l);i<=(r);i++)
#define Clear(a,b) memset(a,b,sizeof(a))
#define inout(x) printf("%d",(x))
#define douin(x) scanf("%lf",&x)
#define strin(x) scanf("%s",(x))
#define LLin(x) scanf("%lld",&x)
#define op operator
#define CSC main
typedef unsigned long long ULL;
typedef const int cint;
typedef long long LL;
using namespace std;
double f(const double &a){return a*a;}
const double eps=1e-8;
void inin(int &ret)
{
    ret=0;int f=0;char ch=getchar();
    while(ch<'0'||ch>'9'){if(ch=='-')f=1;ch=getchar();}
    while(ch>='0'&&ch<='9')ret*=10,ret+=ch-'0',ch=getchar();
    ret=f?-ret:ret;
}
int n;
double xl[11],temp;
double a[11][11],b[11],x[11];
int main()
{
    freopen("in.in","r",stdin);
    freopen("out.out","w",stdout);
    inin(n);
    re(i,1,n)douin(xl[i]);
    re(i,1,n)re(j,1,n)
    {
        douin(temp);
        a[i][j]=2*(temp-xl[j]);
        a[i][n+1]+=f(temp)-f(xl[j]);
    }
    re(i,1,n-1)
    {
        if(abs(a[i][i]<eps))
        re(j,i+1,n)if(abs(a[j][i])>eps)
        {
            re(k,1,n+1)a[i][k]+=a[j][k];
            break;
        }
        re(j,i+1,n)
        {
            if(abs(a[j][i])<eps)continue;
            double bi=a[i][i]/a[j][i];
            re(k,i,n+1)a[j][k]*=bi;
            re(k,i,n+1)a[j][k]-=a[i][k];
        }
    }
    rre(i,n,1)
    {
        x[i]=a[i][n+1]/a[i][i];
        rre(j,i-1,1)a[j][n+1]-=a[j][i]*x[i],a[j][i]=0;
    }
    re(i,1,n)printf("%.3f%c",x[i],i==n?'
':' ');
     return 0;
}