Scripts: radius-of-gyration-mass.py

from chimera import Point, openModels, Molecule, sqdistance
from math import sqrt

for m in openModels.list(modelTypes=[Molecule]):
        masses = [a.element.mass for a in m.atoms]
        com = Point([a.coord() for a in m.atoms], masses)
        sum_sq = 0.0
        for a in m.atoms:
                sum_sq += a.element.mass * sqdistance(a.coord(), com)
        print str(m), "center of mass: %s, radius of gyration: %.3f" % (str(com),
                sqrt(sum_sq / sum(masses)))