struct matrix *
mtx_rref (struct matrix *m_in)
{
struct matrix *m = mtx_copy (m_in);
struct matrix *m_inv = mtx_identity (m->rows);
// remove lower diagonal of the matrix, ie. set to zero by row operations
size_t sum_row, i, j;
float scale = 0.0;
for (sum_row = 0; sum_row < m->rows - 1; sum_row++) // all but the bottom row will be added to the lower row
{
for (i = sum_row + 1; i < m->rows; i++) // each of the lower rows will get added to by the sum_row row
{
scale = m->data[i][sum_row] / m->data[sum_row][sum_row];
for (j = 0; j < m->cols; j++) // sum each element of the row, ignoring zeroes reduces roundoff error, maybe?
{
m->data[i][j] = m->data[i][j] - scale * m->data[sum_row][j];
m_inv->data[i][j] = m_inv->data[i][j] - scale * m_inv->data[sum_row][j];
} // end of j
} // end for i
} // end for sum_row
// remove upper portion
for (sum_row = m->rows-1; sum_row > 0; sum_row--) // all but the top row will be added to the upper row
{
for (i = sum_row - 1; (int)i > -1; i--) // each of the lower rows will get added to by the sum_row row
{
scale = m->data[i][sum_row] / m->data[sum_row][sum_row];
for (j = 0; j < m->cols; j++) // sum each element of the row, need all for inverse matrix
{
m->data[i][j] = m->data[i][j] - scale * m->data[sum_row][j];
m_inv->data[i][j] = m_inv->data[i][j] - scale * m_inv->data[sum_row][j];
} // end of j
} // end for i
} // end for sum_row
for (i = 0; i < m->rows; i++)
{
scale = 1.0 / m->data[i][i];
for (j = 0; j < m->cols; j++)
{
m->data[i][j] *= scale;
m_inv->data[i][j] *= scale;
}
} // end for i
return m_inv;
}
int main(int argc, char**argv) {
#if 1
create_tests(1e-7);
mtx_copy(1e-7);
mtx_diff(1e-1);
mtx_diff(1e-7);
mtxmul_tests(1e-7);
mtxmul_eye_tests(1e-7);
datamul_tests(1e-7);
datamul_eye_tests(1e-7);
#endif
datamul_4_2_tests(1024, 1e-7);
mtxinverse_tests(3e-5);
return pass();
}
