I've been trying to solve the following problem:
Suppose that $G$ is an abelian group, generated by $x_1, x_2, x_3, x_4$, and subject to the relations:
$$4x_1 – 2x_2 – 2x_3 = 0; 8x_1 – 12x_3 + 20x_4 = 0; 6x_1 + 4x_2 – 16x_4 = 0.$$
Write $G$ as a direct product of cyclic groups.
$\textbf{My idea:}$ We can take the free $\mathbb{Z}$-module over $\{x_1, x_2, x_3, x_4\}$, and afterwards we can do quotient by the aforementioned relations. Then we can apply the Fundamental Theorem of Finitely Generated Modules over PIDs. The thing is that after doing quotient by the relations it is hard for me to "grab" the elements of this new abelian group. Any hint?
Best Answer
To compute Smith Normal form we use the following:
So the given group is isomorphic to $\Bbb{Z}_2 \times \Bbb{Z}_2 \times \Bbb{Z}_4$.