[英]Combining gradients from different "networks" in TensorFlow2
我試圖將一些“網絡”組合成一個最終的損失函數。 我想知道我所做的是否“合法”,到目前為止我似乎無法完成這項工作。 我正在使用張量流概率:
主要問題在這里:
# Get gradients of the loss wrt the weights.
gradients = tape.gradient(loss, [m_phis.trainable_weights, m_mus.trainable_weights, m_sigmas.trainable_weights])
# Update the weights of our linear layer.
optimizer.apply_gradients(zip(gradients, [m_phis.trainable_weights, m_mus.trainable_weights, m_sigmas.trainable_weights])
這給了我 None 漸變並拋出應用漸變:
AttributeError: 'list' 對象沒有屬性 'device'
完整代碼:
univariate_gmm = tfp.distributions.MixtureSameFamily(
mixture_distribution=tfp.distributions.Categorical(probs=phis_true),
components_distribution=tfp.distributions.Normal(loc=mus_true,scale=sigmas_true)
)
x = univariate_gmm.sample(n_samples, seed=random_seed).numpy()
dataset = tf.data.Dataset.from_tensor_slices(x)
dataset = dataset.shuffle(buffer_size=1024).batch(64)
m_phis = keras.layers.Dense(2, activation=tf.nn.softmax)
m_mus = keras.layers.Dense(2)
m_sigmas = keras.layers.Dense(2, activation=tf.nn.softplus)
def neg_log_likelihood(y, phis, mus, sigmas):
a = tfp.distributions.Normal(loc=mus[0],scale=sigmas[0]).prob(y)
b = tfp.distributions.Normal(loc=mus[1],scale=sigmas[1]).prob(y)
c = np.log(phis[0]*a + phis[1]*b)
return tf.reduce_sum(-c, axis=-1)
# Instantiate a logistic loss function that expects integer targets.
loss_fn = neg_log_likelihood
# Instantiate an optimizer.
optimizer = tf.keras.optimizers.SGD(learning_rate=1e-3)
# Iterate over the batches of the dataset.
for step, y in enumerate(dataset):
yy = np.expand_dims(y, axis=1)
# Open a GradientTape.
with tf.GradientTape() as tape:
# Forward pass.
phis = m_phis(yy)
mus = m_mus(yy)
sigmas = m_sigmas(yy)
# Loss value for this batch.
loss = loss_fn(yy, phis, mus, sigmas)
# Get gradients of the loss wrt the weights.
gradients = tape.gradient(loss, [m_phis.trainable_weights, m_mus.trainable_weights, m_sigmas.trainable_weights])
# Update the weights of our linear layer.
optimizer.apply_gradients(zip(gradients, [m_phis.trainable_weights, m_mus.trainable_weights, m_sigmas.trainable_weights]))
# Logging.
if step % 100 == 0:
print("Step:", step, "Loss:", float(loss))
有兩個單獨的問題需要考慮。
None
: 通常,如果在GradientTape
監視的代碼中執行非張量流操作,就會發生這種情況。 具體而言,這種擔憂的計算np.log
在neg_log_likelihood
功能。 如果您要更換np.log
與tf.math.log
,梯度應該計算。 盡量不要在“內部”tensorflow 組件中使用 numpy 可能是一個好習慣,因為這可以避免此類錯誤。 對於大多數 numpy 操作,有一個很好的 tensorflow 替代品。
apply_gradients
用於多個可訓練對象: 這主要與apply_gradients
期望的輸入有關。 你有兩個選擇:
第一個選項:調用apply_gradients
三次,每次使用不同的可訓練數據
optimizer.apply_gradients(zip(m_phis_gradients, m_phis.trainable_weights))
optimizer.apply_gradients(zip(m_mus_gradients, m_mus.trainable_weights))
optimizer.apply_gradients(zip(m_sigmas_gradients, m_sigmas.trainable_weights))
另一種方法是創建一個元組列表,如tensorflow 文檔中所示(引用:“grads_and_vars:(梯度,變量)對列表。”)。 這意味着調用類似的東西
optimizer.apply_gradients(
[
zip(m_phis_gradients, m_phis.trainable_weights),
zip(m_mus_gradients, m_mus.trainable_weights),
zip(m_sigmas_gradients, m_sigmas.trainable_weights),
]
)
這兩個選項都要求您拆分漸變。 您可以通過計算梯度並分別為它們編制索引( gradients[0],...
),或者您可以簡單地單獨計算梯度。 請注意,這可能需要您的GradientTape
persistent=True
。
# [...]
# Open a GradientTape.
with tf.GradientTape(persistent=True) as tape:
# Forward pass.
phis = m_phis(yy)
mus = m_mus(yy)
sigmas = m_sigmas(yy)
# Loss value for this batch.
loss = loss_fn(yy, phis, mus, sigmas)
# Get gradients of the loss wrt the weights.
m_phis_gradients = tape.gradient(loss, m_phis.trainable_weights)
m_mus_gradients = tape.gradient(loss, m_mus.trainable_weights)
m_sigmas_gradients = tape.gradient(loss, m_sigmas .trainable_weights)
# Update the weights of our linear layer.
optimizer.apply_gradients(
[
zip(m_phis_gradients, m_phis.trainable_weights),
zip(m_mus_gradients, m_mus.trainable_weights),
zip(m_sigmas_gradients, m_sigmas.trainable_weights),
]
)
# [...]
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