  We develop a network reconstruction model based on entropy maximization
considering the sparsity of networks. We reconstruct the interbank network in
Japan from financial data in individual banks' balance sheets using the
developed reconstruction model from 2000 to 2016. The observed sparsity of the
interbank network is successfully reproduced. We examine the characteristics of
the reconstructed interbank network by calculating important network
attributes. We obtain the following characteristics, which are consistent with
the previously known stylized facts. Although we do not introduce the mechanism
to generate the core and peripheral structure, we impose the constraints to
consider the sparsity that is no transactions within the same bank category
except for major commercial banks, the core and peripheral structure has
spontaneously emerged. We identify major nodes in each community using the
value of PageRank and degree to examine the changing role of each bank
category. The observed changing role of banks is considered a result of the
quantitative and qualitative monetary easing policy started by the Bank of
Japan in April 2013.
