add `y =`
add `y =`

Co-Authored-By: kmaehashi <50f3f01caa053693ce619d596e14b0ff3901ab49@kenichimaehashi.com>
keisuke-umezawa/chainer,wkentaro/chainer,wkentaro/chainer,jnishi/chainer,ktnyt/chainer,ktnyt/chainer,ktnyt/chainer,wkentaro/chainer,ktnyt/chainer,jnishi/chainer,chainer/chainer,okuta/chainer,pfnet/chainer,hvy/chainer,wkentaro/chainer,niboshi/chainer,okuta/chainer,chainer/chainer,okuta/chainer,niboshi/chainer,jnishi/chainer,hvy/chainer,keisuke-umezawa/chainer,keisuke-umezawa/chainer,hvy/chainer,niboshi/chainer,tkerola/chainer,chainer/chainer,okuta/chainer,chainer/chainer,hvy/chainer,niboshi/chainer,keisuke-umezawa/chainer,jnishi/chainer