Il modello sequenziale in Keras

Nel capitolo 3 abbiamo usato componenti dell’API keras in tensorflow per definire una rete neurale, ma senza sfruttarne appieno le potenzialità per semplificare la definizione e l’addestramento del modello. In questo esercizio userai l’API del modello sequenziale di keras per definire una rete neurale da usare per classificare immagini di lettere della lingua dei segni. Userai anche il metodo .summary() per stampare l’architettura del modello, inclusi la forma e il numero di parametri associati a ciascun livello.

Nota che le immagini sono state rimodellate da (28, 28) a (784,), così da poterle usare come input di un livello denso. Inoltre, keras è già stato importato da tensorflow per te.

Questo esercizio fa parte del corso

Introduzione a TensorFlow in Python

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Istruzioni dell'esercizio

Definisci un modello sequenziale keras chiamato model.
Imposta il primo livello a Dense() con 16 nodi e attivazione relu.
Definisci il secondo livello a Dense() con 8 nodi e attivazione relu.
Imposta il livello di output con 4 nodi e funzione di attivazione softmax.

Esercizio pratico interattivo

Prova a risolvere questo esercizio completando il codice di esempio.

# Define a Keras sequential model
____

# Define the first dense layer
model.add(keras.layers.____(____, activation='____', input_shape=(784,)))

# Define the second dense layer
____

# Define the output layer
model.add(keras.layers.Dense(____))

# Print the model architecture
print(model.summary())

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Questo esercizio fa parte del corso

Introduzione a TensorFlow in Python

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Before you can build advanced models in TensorFlow 2, you will first need to understand the basics. In this chapter, you’ll learn how to define constants and variables, perform tensor addition and multiplication, and compute derivatives. Knowledge of linear algebra will be helpful, but not necessary.

Exercise 1: Constants and variables Exercise 2: Defining data as constants Exercise 3: Defining variables Exercise 4: Basic operations Exercise 5: Performing element-wise multiplication Exercise 6: Making predictions with matrix multiplication Exercise 7: Summing over tensor dimensions Exercise 8: Advanced operations Exercise 9: Reshaping tensors Exercise 10: Optimizing with gradients Exercise 11: Working with image data

In this chapter, you will learn how to build, solve, and make predictions with models in TensorFlow 2. You will focus on a simple class of models – the linear regression model – and will try to predict housing prices. By the end of the chapter, you will know how to load and manipulate data, construct loss functions, perform minimization, make predictions, and reduce resource use with batch training.

Exercise 1: Input data Exercise 2: Load data using pandas Exercise 3: Setting the data type Exercise 4: Loss functions Exercise 5: Loss functions in TensorFlow Exercise 6: Modifying the loss function Exercise 7: Linear regression Exercise 8: Set up a linear regression Exercise 9: Train a linear model Exercise 10: Multiple linear regression Exercise 11: Batch training Exercise 12: Preparing to batch train Exercise 13: Training a linear model in batches

The previous chapters taught you how to build models in TensorFlow 2. In this chapter, you will apply those same tools to build, train, and make predictions with neural networks. You will learn how to define dense layers, apply activation functions, select an optimizer, and apply regularization to reduce overfitting. You will take advantage of TensorFlow's flexibility by using both low-level linear algebra and high-level Keras API operations to define and train models.

Exercise 1: Dense layers Exercise 2: The linear algebra of dense layers Exercise 3: The low-level approach with multiple examples Exercise 4: Using the dense layer operation Exercise 5: Activation functions Exercise 6: Binary classification problems Exercise 7: Multiclass classification problems Exercise 8: Optimizers Exercise 9: The dangers of local minima Exercise 10: Avoiding local minima Exercise 11: Training a network in TensorFlow Exercise 12: Initialization in TensorFlow Exercise 13: Defining the model and loss function Exercise 14: Training neural networks with TensorFlow

In the final chapter, you'll use high-level APIs in TensorFlow 2 to train a sign language letter classifier. You will use both the sequential and functional Keras APIs to train, validate, make predictions with, and evaluate models. You will also learn how to use the Estimators API to streamline the model definition and training process, and to avoid errors.

Exercise 1: Definire reti neurali con Keras Exercise 2: Il modello sequenziale in Keras

Esercizio in corso

Exercise 3: Compilare un modello sequenziale Exercise 4: Definire un modello con input multipli Exercise 5: Training e validazione con Keras Exercise 6: Addestramento con Keras Exercise 7: Metriche e validazione con Keras Exercise 8: Rilevamento dell'overfitting Exercise 9: Valutare i modelli Exercise 10: Addestrare modelli con l'API Estimators Exercise 11: Prepararti all'addestramento con Estimators Exercise 12: Definire gli Estimator Exercise 13: Congratulazioni!