BATSE (upper row) and Suzaku (bottom row) GRBs clustered with the CkNN algorithm. Left and right columns: partitioning into two and three groups, respectively; different colours (symbols – circles, squares, and diamonds) symbolise communities. The middle column shows the evolution of the number of communities and VI with Markov time t. The matrix plot in the background displays the VI(t, t′) matrix. Large blocks with small values on the diagonal relate to the number of communities (depicted with the blue line) that is dependent on the Markov time t. The sizes of the matrix blocks indicate the persistence of the corresponding number of communities. The VI is depicted with the green line. Overall, a significant partition is characterised by a large block of small values of the VI(t, t′) matrix, and a low level of the VI.