# Cyclical Learning Rates for Training Neural Networks

"Cyclical Learning Rates for Training Neural Networks" introduced the concept of cyclical learning rates, a novel method of adjusting the learning rate during training.

### Introduction

Typically, when training a neural network, a constant learning rate or a learning rate with a predetermined schedule {such as step decay or exponential decay} is used. However, these approaches may not always be optimal. A learning rate that is too high can cause training to diverge, while a learning rate that is too low can slow down training or cause the model to get stuck in poor local minima.

In this paper, Leslie N. Smith introduced the concept of cyclical learning rates {CLR}, where the learning rate is varied between a lower bound and an upper bound in a cyclical manner. This approach aims to combine the benefits of both high and low learning rates.

### Cyclical Learning Rates

In the CLR approach, the learning rate is cyclically varied between reasonable boundary values. The learning rate increases linearly or exponentially from a lower bound to an upper bound, and then decreases again. This cycle is repeated for the entire duration of the training process.

Mathematically, the learning rate for a given iteration can be calculated as:

[ \text{lr}(t) = \text{lr}{\text{min}} + 0.5 \left( \text{lr}{\text{max}} - \text{lr}{\text{min}} \right) \left( 1 + \cos\left( \frac{T{\text{cur}}}{T} \pi \right) \right) ]

where:

• (\text{lr}(t)) is the learning rate at iteration (t),
• (\text{lr}{\text{min}}) and (\text{lr}{\text{max}}) are the minimum and maximum boundary values for the learning rate,
• (T_{\text{cur}}) is the current number of iterations since the start of the cycle, and
• (T) is the total number of iterations in one cycle.

### Experimental Results

The author tested the CLR method on various datasets and neural network architectures, including CIFAR-10, CIFAR-100, and ImageNet. The results showed that CLR can lead to faster convergence and improved generalization performance compared to traditional learning rate schedules.

### Implications

The concept of cyclical learning rates has significant implications for the field of machine learning:

• Efficiency: CLR can potentially save a considerable amount of time during model training, as it can lead to faster convergence.
• Performance: CLR can improve the generalization performance of the model, potentially leading to better results on the test set.
• Hyperparameter Tuning: CLR reduces the burden of hyperparameter tuning, as it requires less precise initial settings for the learning rate.

### Limitations

While CLR is a powerful tool, it's not without its limitations:

• Cycle Length: Determining the appropriate cycle length can be challenging. While the paper provides some guidelines, it ultimately depends on the specific dataset and model architecture.
• Boundary Values: Similarly, determining the appropriate boundary values for the learning rate can be non-trivial. The paper suggests using a learning rate range test to find these values.

### Conclusion

In conclusion, "Cyclical Learning Rates for Training Neural Networks" made a significant contribution to the field of machine learning by introducing a novel approach to adjust the learning rate during training. The concept of cyclical learning rates has since been widely adopted and implemented in various deep learning libraries.

Tags: Optimization, 2017