dist: DISTANCE ATOMS=3,50 
dist2: DISTANCE ATOMS=1,4
ens: ENSEMBLE ARG=dist,dist2
RESTRAINT AT=0.0 KAPPA=0.0 SLOPE=1.0 ARG=ens.dist
RESTRAINT AT=0.0 KAPPA=0.0 SLOPE=1.0 ARG=ens.dist2
PRINT FILE=COLVAR STRIDE=1 ARG=dist,ens.dist,ens.dist2 FMT=%6.4f
