リカレントニューラルネットワークによる計算結果の検証

#はじめに

• 「詳解 ディープラーニング ~TensorFlow・Kerasによる時系列データ処理~」でRNNを勉強中。Amazon
• RNNの基本的なアルゴリズムを理解するために、TensorFlowによる予測精度と対数損失の計算結果をPythonでも計算してみた。
• 計算を簡略化するため、全てのモデルでBasicRNNCellを使用。
• 例題のモデルは、いずれも固定長を前提としている。

#1. sequence-to-sequenceモデル

• BasicRNNCellを使用したsequence-to-sequenceモデル
• 「3桁の足し算」を答える例題。例えば"24+654"に対して"678"と答える。
• X_validation[N_validation,7,12], Y_validation[N_validation,4,12], input_digits=7, output_digits=4, n_hidden=128

##計算結果の取得

param = []
for a in tf.get_collection(tf.GraphKeys.GLOBAL_VARIABLES):
  param.append(sess.run(a))

##予測精度(acc)と対数損失(loss)の算出

# my library
def softmax(score):
  return np.exp(score) / np.sum(np.exp(score), axis=1, keepdims=True)
def one_hot(score):
  return np.eye(score.shape[1])[np.argmax(score, axis=1)]

w_en = param[0]
c_en = param[1]
v = param[2]
b = param[3]
w_de = param[4]
c_de = param[5]

state = np.zeros([N_validation, n_hidden])
for i in range(input_digits):
  state = np.tanh(np.dot(np.hstack((X_validation[:,i,:], state)), w_en) + c_en)

score = np.dot(state, v) + b
output = [my.softmax(score)]
outhot = [my.one_hot(score)]

for i in range(1, output_digits):
  state = np.tanh(np.dot(np.hstack((outhot[-1], state)), w_de) + c_de)
  score = np.dot(state, v) + b
  output.append(my.softmax(score))
  outhot.append(my.one_hot(score))

output = np.transpose(output, [1,0,2])
acc = np.mean(np.equal(np.argmax(output, 2), np.argmax(Y_validation, 2)))
loss = -np.mean(np.sum(np.log(np.clip(output, 1e-10, 1.0)) * Y_validation, axis=2))

#2. bidirectionalモデル

• BasicRNNCellを使用したstatic_bidirectional_rnn()
• MNISTの画像を長さ28の時系列データとみなして予測する例題。
• X_validation[N_validation,28,28], Y_validation[N_validation,10], n_time=28, n_hidden=128

##予測精度(acc)と対数損失(loss)の算出

w_fw = param[0]
c_fw = param[1]
w_bw = param[2]
c_bw = param[3]
v = param[4]
b = param[5]

output_fw = []
state = np.zeros([N_validation, n_hidden])
for i in range(n_time):
  state = np.tanh(np.dot(np.hstack((X_validation[:,i,:], state)), w_fw) + c_fw)
  output_fw.append(state)

output_bw = []
state = np.zeros([N_validation, n_hidden])
for i in reversed(range(n_time)):
  state = np.tanh(np.dot(np.hstack((X_validation[:,i,:], state)), w_bw) + c_bw)
  output_bw.append(state)

outputs = tuple(np.hstack((fw, bw)) for fw, bw in zip(output_fw, reversed(output_bw)))

score = np.dot(outputs[-1], v) + b
acc = np.mean(np.equal(np.argmax(score, 1), np.argmax(Y_validation, 1)))
loss = -np.mean(np.sum(np.log(np.clip(my.softmax(score), 1e-10, 1.0)) * Y_validation, axis=1))

#3. attentionモデル

• BasicRNNCellに基づいたsequence-to-sequenceモデルにAttentionCellWrapperを適用
• 「3桁の足し算」を答える例題。例えば"24+654"に対して"678"と答える。
• X_validation[N_validation,7,12], Y_validation[N_validation,4,12], input_digits=7, output_digits=4, n_hidden=128
• パラメーターが22個必要。

##予測精度(acc)と対数損失(loss)の算出

w1_en = param[0]
c1_en = param[1]
w2_en = param[2]
c2_en = param[3]
attn_k = param[4]
attn_v = param[5]
attn_w = param[6]
attn_c = param[7]
w3_en = param[8]
c3_en = param[9]
w4_en = param[10]
c4_en = param[11]

state = np.zeros([N_validation, n_hidden])
attns = np.zeros([N_validation, n_hidden])
attn_states = np.zeros([N_validation, input_digits, n_hidden])

def my_attention(state, attn_states):
  hidden_features = np.dot(attn_states, attn_k[0,0])
  y = np.dot(state, attn_w) + attn_c
  y = np.expand_dims(y, 1)
  s = np.sum(attn_v * np.tanh(hidden_features + y), axis=2)
  a = my.softmax(s)
  attns = np.sum(np.expand_dims(a, 2) * attn_states, axis=1)
  return attns

for i in range(input_digits):
  inputs = np.dot(np.hstack((X_validation[:,i,:], attns)), w1_en) + c1_en
  output = np.tanh(np.dot(np.hstack((inputs, state)), w2_en) + c2_en)
  state = output
  attns = my_attention(state, attn_states)
  output = np.dot(np.hstack((output, attns)), w3_en) + c3_en
  attn_states = np.hstack((attn_states[:,1:,:], np.expand_dims(output, 1)))

score = np.dot(output, w4_en) + c4_en
outputs = [my.softmax(score)]
outhots = [my.one_hot(score)]

w1_de = param[12]
c1_de = param[13]
w2_de = param[14]
c2_de = param[15]
attn_k = param[16]
attn_v = param[17]
attn_w = param[18]
attn_c = param[19]
w3_de = param[20]
c3_de = param[21]

for i in range(1, output_digits):
  inputs = np.dot(np.hstack((outhots[-1], attns)), w1_de) + c1_de
  output = np.tanh(np.dot(np.hstack((inputs, state)), w2_de) + c2_de)
  state = output
  attns = my_attention(state, attn_states)
  output = np.dot(np.hstack((output, attns)), w3_de) + c3_de
  attn_states = np.hstack((attn_states[:,1:,:], np.expand_dims(output, 1)))
  score = np.dot(output, w4_en) + c4_en
  outputs.append(my.softmax(score))
  outhots.append(my.one_hot(score))

outputs = np.transpose(outputs, [1,0,2])
acc = np.mean(np.equal(np.argmax(outputs, 2), np.argmax(Y_validation, 2)))
loss = -np.mean(np.sum(np.log(np.clip(outputs, 1e-10, 1.0)) * Y_validation, axis=2))