  Solar active region (AR) 11283 is a very magnetically complex region and it
has produced many eruptions. However, there exists a non-eruptive filament in
the plage region just next to an eruptive one in the AR, which gives us an
opportunity to perform a comparison analysis of these two filaments. The
coronal magnetic field extrapolated using a CESE-MHD-NLFFF code (Jiang & Feng
2013) reveals that two magnetic flux ropes (MFRs) exist in the same
extrapolation box supporting these two filaments, respectively. Analysis of the
magnetic field shows that the eruptive MFR contains a bald-patch separatrix
surface (BPSS) co-spatial very well with a pre-eruptive EUV sigmoid, which is
consistent with the BPSS model for coronal sigmoids. The magnetic dips of the
non-eruptive MFRs match H{\alpha} observation of the non-eruptive filament
strikingly well, which strongly supports the MFR-dip model for filaments.
Compared with the non-eruptive MFR/filament (with a length of about 200 Mm),
the eruptive MFR/filament is much smaller (with a length of about 20 Mm), but
it contains most of the magnetic free energy in the extrapolation box and holds
a much higher free energy density than the non-eruptive one. Both the MFRs are
weakly twisted and cannot trigger kink instability. The AR eruptive MFR is
unstable because its axis reaches above a critical height for torus
instability, at which the overlying closed arcades can no longer confine the
MFR stably. On the contrary, the quiescent MFR is very firmly held by its
overlying field, as its axis apex is far below the torus-instability threshold
height. Overall, this comparison investigation supports that MFR can exist
prior to eruption and the ideal MHD instability can trigger MFR eruption.
