Why is my Python NumPy code faster than C++?

Question

Why is this Python NumPy code,

import numpy as np
import time

k_max = 40000
N = 10000

data = np.zeros((2,N))
coefs = np.zeros((k_max,2),dtype=float)

t1 = t         


        

Answer 1

I tried to understand your Python code and reproduce it in C++. I found that you didn't represent correctly the for-loops in order to do the correct calculations of the coeffs, hence should switch your for-loops. If this is the case, you should have the following:

#include 
#include 
#include 

const int k_max = 40000;
const int N = 10000;

double cos_k, sin_k;

int main(int argc, char const *argv[])
{
    time_t start, stop;
    double data[2][N];
    double coefs[k_max][2];

    time(&start);

    for(int i=0; i

Switching the for-loops gives me: 3 seconds for C++ code, optimized with -O3, while Python code runs at 7.816 seconds.