  We study a reweighting method aiming at numerical studies of QCD at finite
density, in which the conventional Monte-Carlo method cannot be applied
directly. One of the most important problems in the reweighting method is the
overlap problem. To solve it, we propose to perform simulations at several
simulation points and combine their results in the data analyses. In this
report, we introduce this multipoint reweighting method and test if the method
works well by measuring histograms of physical quantities. Using this method,
we calculate the meson masses as continuous functions of the gauge coupling
beta and the hopping parameters kappa in QCD at zero density. We then determine
lines of constant physics in the (beta, kappa) space and evaluate the
derivatives of the lattice spacing with respect to beta and kappa along the
lines of constant physics (inverse of the beta functions), which are needed in
a calculation of the equation of state.
