Respond to some comments from beam2d
Respond to some comments from beam2d

keisuke-umezawa/chainer,keisuke-umezawa/chainer,niboshi/chainer,okuta/chainer,wkentaro/chainer,niboshi/chainer,wkentaro/chainer,tkerola/chainer,chainer/chainer,okuta/chainer,niboshi/chainer,pfnet/chainer,chainer/chainer,hvy/chainer,wkentaro/chainer,keisuke-umezawa/chainer,hvy/chainer,okuta/chainer,okuta/chainer,hvy/chainer,chainer/chainer,chainer/chainer,hvy/chainer,keisuke-umezawa/chainer,wkentaro/chainer,niboshi/chainer