A Comprehensive Guide to Building Deep Learning Models with tf.keras | by Dr. Ernesto Lee | Sep, 2023

Deep learning is a vast domain, and understanding the essential steps to model creation is critical. In this guide, we’ll explore the life cycle of a deep learning model using TensorFlow’s tf.keras and its two prominent APIs: Sequential and Functional.

Crafting a deep learning model comprises five essential steps:

1. Model Definition
2. Model Compilation
3. Model Training (Fitting)
4. Model Evaluation
5. Making Predictions

Let’s delve deeper into each of these.

This is your blueprint. Begin by deciding the kind of model you’re aiming for and then sketch its architecture.

Using the tf.keras API, you’ll be focusing on:

• Determining the layers and their sequence.
• Setting the number of nodes and the activation functions for each layer.
• Intertwining the layers to form a cohesive structure.

Models can be sculpted using either the Sequential or Functional API. We’ll learn more about them later.

# Sample model definition
model = ...

Here, you set the rules of the game. Determine which loss function to minimize, for instance, cross-entropy or mean squared error. Choose your optimizer, be it the classic stochastic gradient descent (SGD) or a modern variant like Adam.

Additionally, decide on performance metrics to monitor during training.

# Sample model compilation
optimizer_instance = SGD(learning_rate=0.01, momentum=0.9)
model.compile(optimizer=optimizer_instance, loss='binary_crossentropy')

The three pivotal loss functions include:

• binary_crossentropy for binary classification.
• sparse_categorical_crossentropy for multi-category classification.
• mse (mean squared error) for regression tasks.

# Another compilation example
model.compile(optimizer='adam', loss='mse')

Don’t forget about metrics. They are crucial for understanding model performance.

# Model compilation with metrics
model.compile(optimizer='adam', loss='binary_crossentropy', metrics=['accuracy'])

For a comprehensive list of supported optimizers, loss functions, and metrics, do explore:

Train your model on your data. Set the number of epochs and choose an appropriate batch size. This phase might be time-consuming, but it’s where the magic happens.

# Fitting the model to data
model.fit(X_train, y_train, epochs=50, batch_size=64)

For a cleaner output, adjust the “verbose” setting.

# Silent training
model.fit(X_train, y_train, epochs=50, batch_size=64, verbose=0)

Once the training is complete, it’s imperative to understand how well your model is performing. This assessment is carried out on a separate dataset, typically known as the test or validation set.

# Evaluating the model's performance
evaluation_metrics = model.evaluate(X_test, y_test, verbose=0)

Here, the model’s predictions are compared with the actual values, providing a tangible measure of the model’s accuracy and effectiveness.

The ultimate aim of any model is to make predictions on new, unseen data. This step is the culmination of all the preceding work.

# Making predictions
predictions = model.predict(new_data)

Whether you’re trying to classify an image, predict sales for the next month, or determine housing prices, the prediction step is where your model gets to showcase its learned prowess.

The Sequential API is akin to building with LEGO blocks — layer by layer, in a linear fashion. It’s especially recommended for those new to the realm of deep learning.

Imagine you are building a model to forecast the popularity of different music genres based on 12 audio features.

# A Sequential model example for music genre popularity prediction
from tensorflow.keras import Sequential
from tensorflow.keras.layers import Dense
# Model definition
music_genre_predictor = Sequential()
music_genre_predictor.add(Dense(20, input_shape=(12,)))
music_genre_predictor.add(Dense(10))
music_genre_predictor.add(Dense(5))  # Five nodes for five music genres

For a more sophisticated touch:

# A deeper Sequential model for the same task
music_genre_predictor = Sequential()
music_genre_predictor.add(Dense(150, input_shape=(12,)))
music_genre_predictor.add(Dense(100))
music_genre_predictor.add(Dense(50))
music_genre_predictor.add(Dense(20))
music_genre_predictor.add(Dense(10))
music_genre_predictor.add(Dense(5))

In this comprehensive guide, we’ve journeyed through the life cycle of a deep learning model using tf.keras. From defining and training to evaluating and predicting, understanding these steps is pivotal. Whether you’re a seasoned data scientist or a budding machine learning enthusiast, these foundational steps are your roadmap. Happy modeling, and may your data always guide you right! 🌟

Now that we’ve charted the path of a deep learning model’s life cycle, it’s crucial to pause and understand some of the terminologies and concepts that were introduced. While it’s tempting to dive headfirst into modeling, having a grasp of these foundational elements can make your journey smoother and more intuitive.

1. Model Definition: Sketching your model’s blueprint.
2. Model Compilation: Setting the optimization rules.
3. Model Training (Fitting): Teaching your model using data.
4. Model Evaluation: Assessing your model’s performance.
5. Making Predictions: Letting your model foresee outcomes on new data.

As a beginner, it’s essential to follow these steps sequentially. However, as you delve deeper, you’ll interact with various hyperparameters and settings. Let’s demystify them.

An epoch refers to one complete forward and backward pass of all the training examples. In simpler terms, it’s one cycle through the entire training dataset. The more epochs you run, the more the model gets to learn from the data. However, too many epochs can lead to overfitting where the model becomes “too perfect” for the training data and performs poorly on new data.

While training, instead of feeding the entire dataset at once, we feed in small chunks or batches. The size of these chunks is the batch size. A smaller batch size often provides a regular update and might converge faster, but it’s computationally intensive. Conversely, a larger batch size is faster but might converge to a sub-optimal solution.

In the context of deep learning, verbose simply refers to how you want your model training’s progress to be displayed. A verbose of 0 will show no logs, 1 will show an animated progress bar, and 2 will display one log line per epoch. It’s more about personal preference and how much feedback you want during training.

The optimizer is the algorithm that adjusts the weights of the model in response to the error from the prediction. Common optimizers include SGD (Stochastic Gradient Descent), Adam, and RMSprop. Each has its strengths and scenarios where they perform best. The optimizer, in essence, defines how quickly the model learns, how it adjusts, and, ultimately, how accurate it becomes.

A loss function, or cost function, quantifies how far off our predictions are from the actual results. It provides a measure of error. During training, the primary goal is to minimize this error. Different problems require different loss functions. For instance, regression problems might use Mean Squared Error, while classification problems use Cross-Entropy.

While the loss function guides the optimization, metrics are used to interpret the model’s performance. For classification problems, accuracy is a common metric. It gives the proportion of correctly predicted classifications in the test data. However, there are other metrics like precision, recall, and F1-score, each giving a different perspective on the model’s performance.

Deep learning, although intricate, follows a systematic path. Before diving deep, ensure you understand each step and component, as they are the building blocks of any model. With this intuition, you’re better equipped to tweak, optimize, and innovate. Remember, each element you introduce or adjust tells your model a bit more about how to approach its learning. Happy tinkering! 🛠️