You can stretch (or shrink) an axis by simply multiplying (or dividing) it by the factor that you want. So, if I were to write

x'' = 2x

where x is my old variable and 2 is the stretch factor I want, I would get a new axis where every point in the old x axis is located twice the distance from the axis in my new variable. Then use this new variable for performing computations on your object.

You can extend this to multiple dimensions. If you want to stretch all dimensions equally, then use the same scaling factor. If however, you want to distort your object, then you can stretch different axes by differing amounts.

Cheers,

Timkin