For vertical shear transformation, the matrix element M11 contains the horizontal shear component, and the element M21 contains the vertical shear component, as follows:
┌ ┐ │ 1 -tan (theta) 0 │ [ x' y' 1 ] = [ x y 1 ] * │ 0 1 0 │ │ 0 0 1 │ └ ┘
For horizontal shear transformation, the matrix element M21 contains the horizontal shear component, and the matrix element M22 contains the vertical shear component, as follows:
┌ ┐ │ 1 0 0 │ [ x' y' 1 ] = [ x y 1 ] * │ -tan theta 1 0 │ │ 0 0 1 │ └ ┘