Cycles - Particle info node - Location + size.. how ?

Hello Blender community.
In my project I work with cycles and I discovered a problem with particles. I would like to make gradient sort of thing, that on one edge of plane I wish to have small particles with low density and on the other edge I would like to have big particles with high density. Is anything like this possible ?

I tried this with Particle Info Node, but I didnt know how to mix Location and Size inputs. Location is vector and Size is not vector (I dont know what Size is - may it be only a number ?).

Add a particle texture and then in the texture panel set it to influence Size and Density.


The Particle Info node can be used to change the particle material depending on its size, location, age etc


Thank You very much, Sir.