GIT quotients of projective spaces

We study the quotients for the diagonal action of SL3(C) on the product of n-fold of P^2(C): we are interested in describing how the quotient changes when we vary the polarization (i.e. the choice of an ample linearized line bundle). We illustrate the different techniques for the construction of a quotient, in particular the numerical criterion for semi-stability and the “elementary transformations” which are resolutions of precisely described singularities (case n = 6)