[模板] 高斯消元

欠了好久的高斯消元

#include<iostream>
#include<cstdio>
#include<cmath>

using namespace std;

const int MAXN=128;

inline int rd(){
  int ret=0,f=1;char c;
  while(c=getchar(),!isdigit(c))f=c=='-'?-1:1;
  while(isdigit(c))ret=ret*10+c-'0',c=getchar();
  return ret*f;
}

double a[MAXN][MAXN],val[MAXN];
int n,w[MAXN];

bool gauss(){
  double eps=1e-6;
  for(int i=1;i<=n;i++){
    double mx=0;int pos=-1;
    for(int j=1;j<=n;j++){
      if(fabs(a[i][j])>mx+eps){mx=fabs(a[i][j]);pos=j;}
    }
    if(pos==-1) return 0;
    w[i]=pos;
    for(int j=1;j<=n;j++){
      if(j==i) continue;
      double t=a[j][pos]/a[i][pos];
      for(int k=1;k<=n+1;k++) a[j][k]-=t*a[i][k];
    }
  }
  for(int i=1;i<=n;i++) val[w[i]]=a[i][n+1]/a[i][w[i]];
  return 1;
}

int main(){
  n=rd();
  for(int i=1;i<=n;i++)
    for(int j=1;j<=n+1;j++)
      a[i][j]=rd();
  if(gauss()==0) return printf("No Solution"),0;
  for(int i=1;i<=n;i++) printf("%.2lf
",val[i]);
  return 0;
}