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Affine transformation, is a combination of linear transformations and translation. A linear transformation can be represented by a matrix. Affine transformation can also be done with a matrix, by adding a dimension to the matrix and the vector. Example:

Suppose we want to This is a linear transformation: {{a,b}, {c,d}} . {x,y} result: {a x+b y, c x+d y} Now, we want to add a translation by {t1,t2}. The matrix now is: {{a,b,t1}, {c,d,t2}, {0,0,1}} . {x,y,1} Result {t1+a x+b y, t2+c x+d y, 1}

Affine transformations are the functions that map straight lines to straight lines.

A linear transformation is a function that preserves all linear combinations; an affine transformation is a function that preserves all affine combinations. An affine combination is a linear combination in which the sum of the coefficients is 1.

2007-05