Gram matrices of reproducing kernel Hilbert spaces over graphs
  In this paper, we introduce the notion of reproducing kernel Hilbert spaces for graphs and the Gram matrices associated with them. Our aim is to investigate the Gram matrices of reproducing kernel Hilbert spaces. We provide several bounds on the entries of the Gram matrices of reproducing kernel Hilbert spaces and characterize the graphs which attain our bounds. 
Michio Seto, Sho Suda, Tetsuji Taniguchi
math.CO math.FA