 The LocalityImprovedString kernel is inspired by the polynomial kernel.
Comparing neighboring characters it puts emphasize on local features.

It can be defined as
K({\bf x},{\bf x'})=\left(\sum_{i=0}^{T-1}\left(\sum_{j=-l}^{+l}w_jI_{i+j}({\bf x},{\bf x'})\right)^{d_1}\right)^{d_2},
where
I_i({\bf x},{\bf x'})=1 
if $x_i=x'_i and 0 otherwise.

