BRIDGE ...
 BRIDGING_ATOMS=1-10 GROUPA=11-20 GROUPB=21-30 
 SWITCH={RATIONAL R_0=1.0} LABEL=w1
... BRIDGE

BRIDGE ...
 BRIDGING_ATOMS=1-10 GROUPA=11-20 GROUPB=21-30
 SWITCH={RATIONAL R_0=1.0} NUMERICAL_DERIVATIVES LABEL=w1num
... BRIDGE

PRINT ARG=w1 FILE=colvar FMT=%8.4f
DUMPDERIVATIVES ARG=w1,w1num FILE=derivatives FMT=%8.4f
