此变分自动编码器因 InvalidArgumentError 失败

Question

这是在 keras 中实现变分自动编码器的代码。训练模型时，执行将在第一个 epoch 结束时终止，如本报告底部所示。

import keras
from keras.layers import Conv2D, Conv2DTranspose, Input, Flatten, Dense, Lambda, Reshape
#from keras.layers import BatchNormalization
from keras.models import Model
from keras.datasets import mnist
from keras import backend as K
import numpy as np
from tensorflow.python.framework.ops import disable_eager_execution
disable_eager_execution()
(x_train, y_train), (x_test, y_test) = mnist.load_data()
x_train = x_train.astype('float32')
x_test = x_test.astype('float32')
x_train = x_train / 255
x_test = x_test / 255
img_width  = x_train.shape[1]
img_height = x_train.shape[2]
num_channels = 1 #MNIST --> grey scale so 1 channel
x_train = x_train.reshape(x_train.shape[0], img_height, img_width, num_channels)
x_test = x_test.reshape(x_test.shape[0], img_height, img_width, num_channels)
input_shape = (img_height, img_width, num_channels)
# ========================
latent_dim = 2 # Number of latent dim parameters

input_img = Input(shape=input_shape, name='encoder_input')
x = Conv2D(32, 3, padding='same', activation='relu')(input_img)
x = Conv2D(64, 3, padding='same', activation='relu',strides=(2, 2))(x)
x = Conv2D(64, 3, padding='same', activation='relu')(x)
x = Conv2D(64, 3, padding='same', activation='relu')(x)

conv_shape = K.int_shape(x) #Shape of conv to be provided to decoder
x = Flatten()(x)
x = Dense(32, activation='relu')(x)
z_mu = Dense(latent_dim, name='z_mu')(x)
z_sigma = Dense(latent_dim, name='z_sigma')(x)

def sample_z(args):
  z_mu, z_sigma = args
  eps = K.random_normal(shape=(K.shape(z_mu)[0], K.int_shape(z_mu)[1]))
  return z_mu + K.exp(z_sigma / 2) * eps

z = Lambda(sample_z, output_shape=(latent_dim, ), name='z')([z_mu, z_sigma])

encoder = Model(input_img, [z_mu, z_sigma, z], name='encoder')
print(encoder.summary())


decoder_input = Input(shape=(latent_dim, ), name='decoder_input')

x = Dense(conv_shape[1]*conv_shape[2]*conv_shape[3], activation='relu')(decoder_input)
x = Reshape((conv_shape[1], conv_shape[2], conv_shape[3]))(x)
x = Conv2DTranspose(32, 3, padding='same', activation='relu',strides=(2, 2))(x)
x = Conv2DTranspose(num_channels, 3, padding='same', activation='sigmoid', name='decoder_output')(x)

decoder = Model(decoder_input, x, name='decoder')
decoder.summary()

z_decoded = decoder(z)

def vae_loss(x, z_decoded):
    x = K.flatten(x)
    z_decoded = K.flatten(z_decoded)
    recon_loss = keras.metrics.binary_crossentropy(x, z_decoded)
    kl_loss = -5e-4 * K.mean(1 + z_sigma - K.square(z_mu) - K.exp(z_sigma), axis=-1)
    return K.mean(recon_loss + kl_loss)

y = decoder(z)


vae = Model(input_img, y, name='vae')

# Compile VAE
vae.compile(optimizer='adam', loss=vae_loss)
vae.summary()

vae.fit(x_train, None, epochs = 10, batch_size = 32, validation_split = 0.2)

它以以下异常结束：

tensorflow.python.framework.errors_impl.InvalidArgumentError：您必须使用 dtype float 和 shape [?,?,?,?] 为占位符张量“decoder_target”提供一个值 [[{{节点解码器_目标}}]]