t1: RMSD REFERENCE=frame_1.dat TYPE=OPTIMAL SQUARED
t2: RMSD REFERENCE=frame_21.dat TYPE=OPTIMAL SQUARED 
t3: RMSD REFERENCE=frame_42.dat TYPE=OPTIMAL SQUARED
p2: FUNCPATHMSD ARG=t1,t2,t3 LAMBDA=500.0 
PRINT ARG=t1,t2,t3,p2.s,p2.z STRIDE=1 FILE=colvar FMT=%8.4f
DUMPDERIVATIVES ARG=p2.s,p2.z STRIDE=1 FILE=deriv FMT=%8.4f
