Translation
To perform translation, you want to leave the x,y components alone while adding the translation factors to x,y. This matrix will do the job:
1 0 0 
Mt =0 1 0 
dx dy 0 
Example:
p = [x y 1]
1 0 0 
p' = p*Mt = [x y 1] * 0 1 0  = [(x+1*dx) (y+1*dy) 1]
dx dy 1 
MATH
Notice the necessity of the 1.0 factor in the lefthand matrix representing the point. Without it, there would be no way to perform translation.
And if you pull out the first two elements, you get
x' = x+dx
y' = y+dy
This is exactly what you wanted.
