An affine transformation is a function (x', y') = f(x, y) givne by
x' = A11 x + A12 y + a1
y' = A21 x + A22 y + a2
or equivalently
f(v) = A v + a
in the matrix notation where v = (x, y), A = (Aij) and a = (a1, a2).
The set of all affine transformation on ℝ2 is called the Affine group and denoted by Aff(2) = ℝ × GL(2, ℝ). The orientation preserving subgroup is denoted by Aff+(2) = ℝ × GL+(2, ℝ).
Visit https://ggorr.github.io/AffineTorus/