forget_example.py

import numpy

import chainer
import chainer.functions as F
import chainer.links as L


class LongChain(chainer.Chain):
    def __init__(self):
        super(LongChain, self).__init__()

        links = []
        for i in range(100):
            links += [('conv{}'.format(i + 1),
                       L.Convolution2D(100, 100, 1, initialW=0.01))]

        for link in links:
            self.add_link(*link)

        self.links = links

    def __call__(self, x):
        for i in range(0, len(self.links), 10):
            links = self.links[i:i+10]
            class n_conv(object):
                def __init__(self, links):
                    self.links = links

                def __call__(self, x):
                    for name, f in self.links:
                        x = f(x)
                    return x

            x = F.forget(n_conv(links), x)
        return x


m = LongChain()
x = chainer.Variable(numpy.random.uniform(-1, 1, (100, 100, 100)).astype('f')[None, ...])
y = F.sum(m(x))
m.zerograds()
y.backward()
print(m.conv1.W.grad)