simulations [@Giacomazzo:2010; @Rezzolla:2011], even at very high resolution [@Kiuchi2014]. Finally, progress has taken place also on the derivation of improved numerical techniques, such as those in Ref. [@Etienne2012a], where the significant advantages of a vector-potential approach and of a Lorentz gauge were discussed.

All of the works mentioned above have been carried out within the ideal-magnetohydrodynamic (IMHD) approximation, in which the electrical conductivity is assumed to be infinite. Under these conditions, the magnetic flux is conserved and the magnetic field is frozen into the fluid, being simply advected with it. This is a very good approximation for the stellar interior before the merger because it neglects any effect of resistivity on the dynamics of the plasma. After the merger, however, there will be spatial regions with very hot plasma where the electrical conductivity is finite and the resistive effects, most notably, magnetic reconnection, will take place.

An obvious improvement over the IMHD description is the use of the general-relativistic resistive-magnetohydrodynamic (RMHD) equations, which provide a complete magnetohydrodynamic (MHD) description of regions with a high conductivity, such as the stellar interiors, and of regions with small conductivity, such as the electrovacuum exterior. Furthermore, when the conductivity is set to zero, it 