为什么简单的计算结果在Python和C++中不同？

Question

我使用一个简单的数据集来计算x和y值之间的线性回归。我用Python和C++编写了代码。然而，由于操作过程中的舍入（我相信），输出差异很大。最低可运行产品：

cpp代码：

void linear_regression1(){
    vector<int> independent;
    independent.push_back(60300);
    independent.push_back(60302);
    independent.push_back(60302);
    independent.push_back(60290);
    independent.push_back(60292);
    independent.push_back(60290);

    vector<double> dependent_mid;
    dependent_mid.push_back(143.5);
    dependent_mid.push_back(143.5);
    dependent_mid.push_back(143.5);
    dependent_mid.push_back(142.5);
    dependent_mid.push_back(142.5);
    dependent_mid.push_back(142.5);




    double sumX=0, sumX2=0, sumY=0, sumXY=0, a, b;

    int n = independent.size();



    for(int i=0;i<n;i++)
    {
        sumX = sumX + independent[i];
        sumX2 = sumX2 + independent[i]*independent[i];
        sumY = sumY + dependent_mid[i];
        sumXY = sumXY + independent[i]*dependent_mid[i];
        //cout<<sumXY<<endl;
    }
    /* Calculating a and b */
    b = (n*sumXY-sumX*sumY)/(n*sumX2-sumX*sumX);
    a = (sumX2*sumY-sumX*sumXY)/(sumX2*n-sumX*sumX);

    /* Displaying value of a and b */
    cout<<"Equation of best fit is: y = "<< a <<" + "<< b<<"x";

}

python代码：

import numpy as np  
import matplotlib.pyplot as plt  
import seaborn as seabornInstance 
from sklearn.model_selection import train_test_split 
from sklearn.linear_model import LinearRegression
from sklearn import metrics
%matplotlib inline

data = {'x': [60300, 60302, 60300, 60302, 60290, 60292],
        'y_mid': [143.5, 143.5, 143.5, 143.5, 142.5, 142.5]
        }

df = pd.DataFrame(data, columns = ['x', 'y_mid'])



X = df['x']
y = df['y_mid']
sumX=0 
sumX2=0
sumY=0
sumXY=0

for i in range(len(X)):
    sumX = sumX + X[i]
    sumX2 = sumX2 + X[i]*X[i]
    sumY = sumY + y[i]
    sumXY = sumXY + X[i]*y[i]


b = (len(X)*sumXY-sumX*sumY)/(len(X)*sumX2-sumX*sumX)
a = (sumX2*sumY-sumX*sumXY)/(sumX2*len(X)-sumX*sumX)

print(a)
print(b)

我知道Python的结果是正确的

Answer 1

代码中存在整数溢出问题：60'300*60'300=3'636'090'000，而int通常为4字节长，只能保存[-2^31，2^31-1]=[-2'147'483'648，2'147'483'647]范围内的值

Python的整数不会溢出