Upper and lower bounds of symmetric division deg index

Symmetric division deg index is one of the 148 discrete adriatic indices that showed good predictive properties on the testing sets provided by international academy of mathematical chemistry. symmetric division deg index is defined by sdd(g) = sume left( frac{min{d_u,d_v}}{max{d_u,d_v}} + frac{max{d_u,d_v}}{min{d_u,d_v}} right), where d_i is the degree of vertex i in graph g. where di is the degree of vertex i in graph g. in this paper we provide lower and upper bounds of symmetric division deg index in some classes of graphs and determine the corresponding extremal graphs.