change to get dtype from parameters
change to get dtype from parameters

okuta/chainer,niboshi/chainer,okuta/chainer,niboshi/chainer,hvy/chainer,chainer/chainer,okuta/chainer,wkentaro/chainer,okuta/chainer,hvy/chainer,wkentaro/chainer,hvy/chainer,wkentaro/chainer,niboshi/chainer,wkentaro/chainer,chainer/chainer,hvy/chainer,chainer/chainer,chainer/chainer,pfnet/chainer,niboshi/chainer