imresize with bilinear mode

How does Matlab's imresize(...bilinear...) algorithm work, how does it choose the sampling points?

I am using a simple vector:

>> I = [1:5];

>> J = imresize(I, [1 7],'bilinear')

J =

      1.0000    1.5714    2.2857    3.0000    3.7143    4.4286    5.0000

Manual computation using the formula from http://en.wikipedia.org/wiki/Bilinear_interpolation : 1 5/3 7/3 3 11/3 13/3 5

Things get even more confusing when I apply a scaling factor:

>> J = imresize(I, 1.3 , 'bilinear')

J =

      1.0000    1.6538    2.4231    3.1923    3.9615    4.7308    5.0000
      1.0000    1.6538    2.4231    3.1923    3.9615    4.7308    5.0000