## C++, , qr_decomposition.cpp

``````/**
* @file
* \brief Program to compute the [QR
* decomposition](https://en.wikipedia.org/wiki/QR_decomposition) of a given
* matrix.
* \author [Krishna Vedala](https://github.com/kvedala)
*/

#include <array>
#include <cmath>
#include <cstdlib>
#include <ctime>
#include <iostream>

#include "./qr_decompose.h"

using qr_algorithm::qr_decompose;
using qr_algorithm::operator<<;

/**
* main function
*/
int main(void) {
unsigned int ROWS, COLUMNS;

std::cout << "Enter the number of rows and columns: ";
std::cin >> ROWS >> COLUMNS;

std::cout << "Enter matrix elements row-wise:\n";

std::valarray<std::valarray<double>> A(ROWS);
std::valarray<std::valarray<double>> Q(ROWS);
std::valarray<std::valarray<double>> R(COLUMNS);
for (int i = 0; i < std::max(ROWS, COLUMNS); i++) {
if (i < ROWS) {
A[i] = std::valarray<double>(COLUMNS);
Q[i] = std::valarray<double>(COLUMNS);
}
if (i < COLUMNS) {
R[i] = std::valarray<double>(COLUMNS);
}
}

for (int i = 0; i < ROWS; i++)
for (int j = 0; j < COLUMNS; j++) std::cin >> A[i][j];

std::cout << A << "\n";

clock_t t1 = clock();
qr_decompose(A, &Q, &R);
double dtime = static_cast<double>(clock() - t1) / CLOCKS_PER_SEC;

std::cout << Q << "\n";
std::cout << R << "\n";
std::cout << "Time taken to compute: " << dtime << " sec\n ";

return 0;
}
``````