The evolution of the Erd\H{o}s-R\'enyi (ER) network by adding edges can be
viewed as a cluster aggregation process. Such ER processes can be described by
a rate equation for the evolution of the cluster-size distribution with the
connection kernel Kij∼ij, where ij is the product of the sizes of
two merging clusters. Here, we study more general cases in which Kij is
sub-linear as Kij∼(ij)ω with 0≤ω<1/2; we find
that the percolation transition (PT) is discontinuous. Moreover, PT is also
discontinuous when the ER dynamics evolves from proper initial conditions. The
rate equation approach for such discontinuous PTs enables us to uncover the
mechanism underlying the explosive PT under the Achlioptas process.Comment: 5 pages, 5 figure