  The recent work, Nemoto and Sasa [Phys. Rev. E, 83: 030105(R) (2011)], has
shown that large deviations of the current characterizing a nonequilibrium
system are obtained by observing the typical current for a modified system
specified by a variational principle. In the present study, we will give a
generalized version of the Nemoto-Sasa study by extracting a hidden
mathematical structure from the fluctuation-response relation which is
well-known in statistical mechanics. Here, the minimization of the
Kullback-Leibler divergence plays an essential role.
