The dangers of local minima

Consider the plot of the following loss function, loss_function(), which contains a global minimum, marked by the dot on the right, and several local minima, including the one marked by the dot on the left.

The graph is of a single variable function that contains multiple local minima and a global minimum.

In this exercise, you will try to find the global minimum of loss_function() using keras.optimizers.SGD(). You will do this twice, each time with a different initial value of the input to loss_function(). First, you will use x_1, which is a variable with an initial value of 6.0. Second, you will use x_2, which is a variable with an initial value of 0.3. Note that loss_function() has been defined and is available.

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Introduction to TensorFlow in Python

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Set opt to use the stochastic gradient descent optimizer (SGD) with a learning rate of 0.01.
Perform minimization using the loss function, loss_function(), and the variable with an initial value of 6.0, x_1.
Perform minimization using the loss function, loss_function(), and the variable with an initial value of 0.3, x_2.
Print x_1 and x_2 as numpy arrays and check whether the values differ. These are the minima that the algorithm identified.

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Probeer deze oefening eens door deze voorbeeldcode in te vullen.

# Initialize x_1 and x_2
x_1 = Variable(6.0,float32)
x_2 = Variable(0.3,float32)

# Define the optimization operation
opt = keras.optimizers.____(learning_rate=____)

for j in range(100):
	# Perform minimization using the loss function and x_1
	opt.minimize(lambda: loss_function(____), var_list=[____])
	# Perform minimization using the loss function and x_2
	opt.minimize(lambda: ____, var_list=[____])

# Print x_1 and x_2 as numpy arrays
print(____.numpy(), ____.numpy())

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Deze oefening maakt deel uit van de cursus

Introduction to 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

Huidige oefening

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: Defining neural networks with Keras Exercise 2: The sequential model in Keras Exercise 3: Compiling a sequential model Exercise 4: Defining a multiple input model Exercise 5: Training and validation with Keras Exercise 6: Training with Keras Exercise 7: Metrics and validation with Keras Exercise 8: Overfitting detection Exercise 9: Evaluating models Exercise 10: Training models with the Estimators API Exercise 11: Preparing to train with Estimators Exercise 12: Defining Estimators Exercise 13: Congratulations!