Improve numerical grad performance on GPU
Improve numerical grad performance on GPU

okuta/chainer,ktnyt/chainer,okuta/chainer,hvy/chainer,ktnyt/chainer,keisuke-umezawa/chainer,ronekko/chainer,aonotas/chainer,rezoo/chainer,keisuke-umezawa/chainer,ktnyt/chainer,ktnyt/chainer,wkentaro/chainer,okuta/chainer,keisuke-umezawa/chainer,hvy/chainer,wkentaro/chainer,tkerola/chainer,niboshi/chainer,jnishi/chainer,jnishi/chainer,wkentaro/chainer,niboshi/chainer,chainer/chainer,hvy/chainer,jnishi/chainer,keisuke-umezawa/chainer,kashif/chainer,pfnet/chainer,niboshi/chainer,jnishi/chainer,wkentaro/chainer,chainer/chainer,okuta/chainer,chainer/chainer,chainer/chainer,hvy/chainer,anaruse/chainer,niboshi/chainer