plist = 'H5P_DEFAULT';
fid = H5F.create('myfile.h5','H5F_ACC_TRUNC',plist,plist);
gid = H5G.create(fid,'/g1',plist);
H5O.set_comment(gid,'This is a group comment.');
H5G.close(gid);
H5F.close(fid);