# Today I Learned

Some of the things I've learned every day since Oct 10, 2016

## 9: Unimodular Matrices

unimodular matrix is a square integer matrix with determinant $\pm 1$.

A unimodular matrix has an inverse which is itself unimodular. Furthermore, since the identity matrix $I_n$ as well as the product of any 2 unimodular matrices are all unimodular, the set of $n \times n$ unimodular matrices forms a group under multiplication, denoted $G L_n (\mathbb{Z})$.