A transformation 
is unimodular if the determinant
of the matrix 
satisfies
 |
A necessary and sufficient condition that a linear transformation transform a lattice to itself is that the transformation be unimodular.
If 
is a complex number, then the transformation
 |
is called a unimodular if 
, 
, 
, and 
are integers with 
. The set of all unimodular transformations forms a group called the modular group.
