## C, , qr_decomposition.c

``````/**
* @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 <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include "qr_decompose.h"

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

printf("Enter the number of rows and columns: ");
scanf("%u %u", &ROWS, &COLUMNS);
if (ROWS < COLUMNS)
{
fprintf(stderr,
"Number of rows must be greater than or equal to "
"number of columns.\n");
return -1;
}

printf("Enter matrix elements row-wise:\n");

A = (double **)malloc(ROWS * sizeof(double *));
for (int i = 0; i < ROWS; i++)
A[i] = (double *)malloc(COLUMNS * sizeof(double));

for (int i = 0; i < ROWS; i++)
for (int j = 0; j < COLUMNS; j++) scanf("%lf", &A[i][j]);

print_matrix(A, ROWS, COLUMNS);

double **R = (double **)malloc(sizeof(double *) * ROWS);
double **Q = (double **)malloc(sizeof(double *) * ROWS);
if (!Q || !R)
{
perror("Unable to allocate memory for Q & R!");
return -1;
}
for (int i = 0; i < ROWS; i++)
{
R[i] = (double *)malloc(sizeof(double) * COLUMNS);
Q[i] = (double *)malloc(sizeof(double) * ROWS);
if (!Q[i] || !R[i])
{
perror("Unable to allocate memory for Q & R.");
return -1;
}
}

clock_t t1 = clock();
qr_decompose(A, Q, R, ROWS, COLUMNS);
double dtime = (double)(clock() - t1) / CLOCKS_PER_SEC;

print_matrix(R, ROWS, COLUMNS);
print_matrix(Q, ROWS, COLUMNS);
printf("Time taken to compute: %.4g sec\n", dtime);

for (int i = 0; i < ROWS; i++)
{
free(A[i]);
free(R[i]);
free(Q[i]);
}
free(A);
free(R);
free(Q);
return 0;
}
``````