We present a set of expressions for evaluating energies and forces bet
ween particles interacting logarithmically in a finite two-dimensional
system with periodic boundary conditions. The formalism can be used f
or fast and accurate, dynamical or Monte Carlo, simulations of interac
ting line charges or interactions between point and line charges. The
expressions are shown to converge to usual computer accuracy (similar
to 10(-16)) by adding only few terms in a single sum of standard trigo
nometric functions.