from cs231n.rnn_layers import lstm_forward, lstm_backward
np.random.seed(231)
N, D, T, H = 2, 3, 10, 6
x = np.random.randn(N, T, D)
h0 = np.random.randn(N, H)
Wx = np.random.randn(D, 4 * H)
Wh = np.random.randn(H, 4 * H)
b = np.random.randn(4 * H)
out, cache = lstm_forward(x, h0, Wx, Wh, b)
dout = np.random.randn(*out.shape)
dx, dh0, dWx, dWh, db = lstm_backward(dout, cache)
fx = lambda x: lstm_forward(x, h0, Wx, Wh, b)[0]
fh0 = lambda h0: lstm_forward(x, h0, Wx, Wh, b)[0]
fWx = lambda Wx: lstm_forward(x, h0, Wx, Wh, b)[0]
fWh = lambda Wh: lstm_forward(x, h0, Wx, Wh, b)[0]
fb = lambda b: lstm_forward(x, h0, Wx, Wh, b)[0]
dx_num = eval_numerical_gradient_array(fx, x, dout)
dh0_num = eval_numerical_gradient_array(fh0, h0, dout)
dWx_num = eval_numerical_gradient_array(fWx, Wx, dout)
dWh_num = eval_numerical_gradient_array(fWh, Wh, dout)
db_num = eval_numerical_gradient_array(fb, b, dout)
print('dx error: ', rel_error(dx_num, dx))
print('dh0 error: ', rel_error(dh0_num, dh0))
def loss(self, features, captions):
"""
Compute training-time loss for the RNN. We input image features and
ground-truth captions for those images, and use an RNN (or LSTM) to compute
loss and gradients on all parameters.
Inputs:
- features: Input image features, of shape (N, D)
- captions: Ground-truth captions; an integer array of shape (N, T) where
each element is in the range 0 <= y[i, t] < V
Returns a tuple of:
- loss: Scalar loss
- grads: Dictionary of gradients parallel to self.params
"""
# Cut captions into two pieces: captions_in has everything but the last word
# and will be input to the RNN; captions_out has everything but the first
# word and this is what we will expect the RNN to generate. These are offset
# by one relative to each other because the RNN should produce word (t+1)
# after receiving word t. The first element of captions_in will be the START
# token, and the first element of captions_out will be the first word.
captions_in = captions[:, :-1]
captions_out = captions[:, 1:]
# You'll need this
mask = (captions_out != self._null)
# Weight and bias for the affine transform from image features to initial
# hidden state
W_proj, b_proj = self.params['W_proj'], self.params['b_proj']
# Word embedding matrix
W_embed = self.params['W_embed']
# Input-to-hidden, hidden-to-hidden, adn biases for the RNN
Wx, Wh, b = self.params['Wx'], self.params['Wh'], self.params['b']
# Weight and bias for the hidden-to-vocab transformation
W_vocab, b_vocab = self.params['W_vocab'], self.params['b_vocab']
loss, grads = 0.0, {}
############################################################################
# TODO: Implement the forward and backward passes for the CaptioningRNN. #
# In the forward pass you will need to do the following: #
# (1) Use an affine transformation to compute the initial hidden state #
# from the image features. This should produce an array of shape (N, H)#
# (2) Use a word embedding layer to transform the words in captions_in #
# from indices to vectors, giving an array of shape (N, T, W). #
# (3) Use either a vanilla RNN or LSTM (depending on self.cell_type) to #
# process the sequence of input word vectors and produce hidden state #
# vectors for all timesteps, producing an array of shape (N, T, H). #
# (4) Use a (temporal) affine transformation to compute scores over the #
# vocabulary at every timestep using the hidden states, giving an #
# array of shape (N, T, V). #
# (5) Use (temporal) softmax to compute loss using captions_out, ignoring #
# the points where the output word is <NULL> using the mask above. #
# #
# In the backward pass you will need to compute the gradient of the loss #
# with respect to all model parameters. Use the loss and grads variables #
# defined above to store loss and gradients; grads[k] should give the #
# gradients for self.params[k]. #
############################################################################
# pass
N, _ = features.shape
h0 = np.dot(features,W_proj) + b_proj # (1)
word_vec, word_vec_cache = word_embedding_forward(captions_in, W_embed) # (2)
if self.cell_type == 'rnn':
h, h_cache = rnn_forward(x= word_vec, h0= h0, Wx= Wx, Wh= Wh, b= b) # (3)
out, out_cache = temporal_affine_forward(x= h, w= W_vocab, b= b_vocab) # (4)
mask = (captions_out!=self._null)
loss, dx = temporal_softmax_loss(x= out, y= captions_out, mask= mask, verbose=False)
dh, grads['W_vocab'], grads['b_vocab'] = temporal_affine_backward(dx, out_cache)
dcaption_in, dh0, grads['Wx'], grads['Wh'], grads['b'] = rnn_backward(dh, h_cache)
grads['W_embed'] = word_embedding_backward(dcaption_in, word_vec_cache)
grads['W_proj'] = np.dot(features.T, dh0)
grads['b_proj'] = np.sum(dh0, axis=0)
else:
if self.cell_type == 'lstm':
h, h_cache = lstm_forward(x= word_vec, h0= h0, Wx= Wx, Wh= Wh, b= b) # (2)
out, out_cache = temporal_affine_forward(x= h, w= W_vocab, b= b_vocab)
mask = (captions_out!=self._null)
loss, dx = temporal_softmax_loss(x= out, y= captions_out, mask= mask, verbose= False)
dh, grads['W_vocab'], grads['b_vocab'] = temporal_affine_backward(dx, out_cache)
dcaption_in, dh0, grads['Wx'], grads['Wh'], grads['b'] = lstm_backward(dh, h_cache)
grads['W_embed'] = word_embedding_backward(dcaption_in, word_vec_cache)
grads['W_proj'] = np.dot(features.T, dh0)
grads['b_proj'] = np.sum(dh0, axis=0)
else:
print('Unknow type')
############################################################################
# END OF YOUR CODE #
############################################################################
return loss, grads
