高斯消元板子求助，一直WA#9#8

qwq2519 @ 2021-10-04 09:08:27

#include<iostream>
#include<cstdio>
#include<bits/stdc++.h>
#define rep(i,j,k) for(register int i(j);i<=k;++i)
#define drp(i,j,k) for(register int i(j);i>=k;--i)
#define repg(x) for(register int i(G.head[x]);i;i=G.next[i])
#define bug cout<<"~~~~~~~~~~~~~"<<'\n';
#define bugout(x) cout<<x<<'\n';
using std::cin;
using std::cout;
typedef long long lxl;
template<typename T> 
inline T  max( T a, T b) {
    return a > b ? a : b;
}
template<typename T> 
inline T  min( T a, T b) {
    return a < b ? a : b;
}
const double eps=1e-7;
const int N=57;
int n;
double a[N][N],ans[N];
int main() {
    std::ios::sync_with_stdio(false);
    cin>>n;
    rep(i,1,n){
        rep(j,1,n+1){
            cin>>a[i][j];
        }
    }

    rep(i,1,n){
        int pos=i;
        rep(j,i+1,n){
            if(fabs(a[pos][i])<=fabs(a[j][i])) pos=j;
        }

        if(fabs(a[pos][i])<eps){
            if(a[pos][n+1]) cout<<-1<<'\n';
            else 
            cout<<0<<'\n';
            return 0;
        }

        if(i!=pos) std::swap(a[i],a[pos]);

        double div(a[i][i]);
        rep(j,i,n+1){
            a[i][j]/=div;
        }

        rep(j,i+1,n){
            div=a[j][i];
            rep(k,i,n+1){
                a[j][k]-=a[i][k]*div;
            }
        }   
    }   

    ans[n]=a[n][n+1];
    drp(i,n-1,1){
        ans[i]=a[i][n+1];
        rep(j,i+1,n){
            ans[i]-=a[i][j]*ans[j];
        }
    }
    rep(i,1,n){
        cout<<"x"<<i<<"="<<std::fixed<<std::setprecision(2)<<ans[i]<<'\n';
    }   

    return 0;
}

by qwq2519 @ 2021-10-04 09:32:31

#include<iostream>
#include<cstdio>
#include<bits/stdc++.h>
#define rep(i,j,k) for(register int i(j);i<=k;++i)
#define drp(i,j,k) for(register int i(j);i>=k;--i)
#define repg(x) for(register int i(G.head[x]);i;i=G.next[i])
#define bug cout<<"~~~~~~~~~~~~~"<<'\n';
#define bugout(x) cout<<x<<'\n';
using std::cin;
using std::cout;
typedef long long lxl;
template<typename T>
inline T  max( T a, T b) {
    return a > b ? a : b;
}
template<typename T>
inline T  min( T a, T b) {
    return a < b ? a : b;
}
const double eps = 1e-7;
const int N = 57;
int n;
double a[N][N], ans[N];
int main() {
    std::ios::sync_with_stdio(false);
    cin >> n;
    rep(i, 1, n) {
        rep(j, 1, n + 1) {
            cin >> a[i][j];
        }
    }

    rep(i, 1, n) {
        int pos = i;
        rep(j, i + 1, n) {
            if(fabs(a[pos][i]) <= fabs(a[j][i])) pos = j;
        }

        if(i != pos) std::swap(a[i], a[pos]);

        if(fabs(a[i][i]) < eps) {
            if(fabs(a[i][n + 1] ) > eps)
                cout << -1 << '\n';
            else
                cout << 0 << '\n';
            return 0;
        }

        double div(a[i][i]);
        rep(j, i, n + 1) {
            a[i][j] /= div;
        }

        rep(j, i + 1, n) {
            div = a[j][i];
            rep(k, i, n + 1) {
                a[j][k] -= a[i][k] * div;
            }
        }
    }

    ans[n] = a[n][n + 1];
    drp(i, n - 1, 1) {
        ans[i] = a[i][n + 1];
        rep(j, i + 1, n) {
            ans[i] -= a[i][j] * ans[j];
        }
    }
    rep(i, 1, n) {
        cout << "x" << i << "=" << std::fixed << std::setprecision(2) << ans[i] << '\n';
    }

    return 0;
}

by qwq2519 @ 2021-10-04 10:37:49

我发现

int pos = i;
        rep(j, i + 1, n) {
            if(fabs(a[pos][i]) <= fabs(a[j][i])) pos = j;
        }

等于号去掉WAon#4,8 不去掉WA on#8,9 ..所以随机化？

by qwq2519 @ 2021-10-04 10:58:18

现在又改了，变成WA on#9,#10