Sat. Dec 2nd, 2023
How to Optimise Neural Networks with Architecture Search

Are you looking to optimize the performance of your neural networks? If so, neural architecture search (NAS) might be the answer. NAS is an automated process used to create optimal architectures for neural networks.

It helps to reduce the time and effort it takes to design and configure complex network architectures. In this blog post, we will discuss the fundamentals of neural architecture search methods and how it can be used to optimize neural networks.

What is Neural Architecture Search (NAS)?

In short, Neural Architecture Search (NAS) is a technique used to automate the process of designing neural networks, which are in turn utilized to achieve tasks in the realms of image recognition and natural language processing, among others.

NAS algorithms use an automated search process to explore the search space of possible architectures and evaluate them in terms of their performance on a task. The goal of the search is to identify the optimal architecture among the many possibilities.

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NAS algorithms are designed to solve a specific problem, so they take into consideration various factors such as the number of layers, the types of neurons and the parameters that determine how neurons interact with each other.

NAS algorithms start by defining the problem that needs to be solved and then create a search space. The search space consists of all the possible architectures that could potentially solve the given problem.

The NAS algorithm then evaluates all the possible architectures using an objective function, which measures their performance on the task. Finally, it selects the best architecture from the list of potential architectures and outputs it as the solution.

NAS algorithms have been used in many fields such as computer vision, natural language processing, robotics, and drug discovery. In addition, NAS algorithms can be used for optimizing existing models or creating completely new ones from scratch.

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These algorithms have revolutionized the way machines learn, allowing them to achieve greater accuracy and efficiency than ever before.

Problem Definition

Neural architecture search (NAS) is a relatively new area of research that focuses on automating the design of neural networks.

It involves using a search algorithm to automatically optimize the network’s architecture and parameters for a given task. The goal of NAS is to find an optimal network architecture that can provide the best possible performance in terms of accuracy, speed, or any other desired metric.

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NAS Project :

When beginning a NAS project, it’s important to clearly define the problem that needs to be solved. This involves understanding the data set, the task the model will need to perform, the metrics that should be used to measure success, and the type of neural network architecture to use.

The search space for a NAS project must be carefully considered. It defines the possible solutions that the search algorithm can explore.

Typically, this search space includes neural network architectures as well as their associated hyperparameters such as learning rate, regularization, optimizer, and so on.
The search strategy is also essential.

This defines how the search algorithm will traverse through the search space to find the optimal solution. The search strategy can involve techniques such as grid search, random search, or evolutionary algorithms.

Finally, it is important to choose an appropriate search algorithm. These algorithms can vary greatly in complexity and have their own pros and cons.

Popular examples include gradient-based algorithms, reinforcement learning methods, Bayesian optimization, and genetic algorithms.

Search Space

When it comes to neural architecture search, the search space refers to the set of architectures available for exploration. Different types of search spaces exist that can be used depending on the type of problem.

For example

Some problems may require a more focused search space such as those used in cell-based NAS, while others may need a more open search space such as those used in macro-architecture NAS.

In cell-based NAS, the search space is typically composed of the set of neural network modules (or ‘cells’) that can be used to create the target network architecture.

This search space can be constructed from a variety of predefined building blocks and operations including convolutional layers, pooling layers, normalization layers, activation functions, etc. The cell-based search space can also be further limited by imposing constraints on the parameters associated with each cell, such as number of filters or receptive field sizes.

In macro-architecture NAS, the search space is comprised of a larger set of predefined network structures and components such as convolutional layers, fully connected layers, pooling layers, activation functions, etc.

In addition to these structural elements, various hyperparameters such as learning rate and optimizer may also be included in the search space.

In either case, it is important to carefully construct an appropriate search space that takes into account the problem at hand and its inherent limitations.

This is an important step in ensuring that the resulting neural architectures are optimized for their intended task.

Search Strategy

When it comes to Neural Architecture Search (NAS), there is no single definitive search strategy that works best for all problems.

Each task and dataset have their own specific requirements, so it’s important to choose the right search strategy to optimize performance.

There are two primary strategies when it comes to NAS: reinforcement learning and evolutionary algorithms. Both strategies have their own strengths and weaknesses and should be selected based on the specific problem at hand.

Reinforcement learning is a trial-and-error approach that uses feedback to drive its decisions.

The agent evaluates the performance of each architecture, receives rewards for positive results, and takes corrective action to improve results.

This approach can be computationally expensive, but is particularly useful for problems with complex search spaces.

Evolutionary algorithms work by simulating natural selection. They generate a population of architectures, evaluate their performance, then use selection and mutation operators to create the next generation of architectures.

This approach can be faster than reinforcement learning since it relies on fewer trials, but is also less accurate since there are more unknowns in each new generation.

No matter which search strategy is chosen, the key to successful NAS is to properly define the search space and evaluate architectures.

If an architecture is too complex or too simple, it won’t provide good results. The best search strategies are those that take the time to explore different architectures and find the best ones for the task at hand.

Search Algorithms

Neural architecture search (NAS) algorithms are used to identify optimal neural network architectures from a predefined set of components. These algorithms allow for the exploration of the large search space for neural networks and enable the optimization of models for a specific task.

The most commonly used search algorithms for NAS are Reinforcement Learning (RL), Evolutionary Algorithms (EA) and Bayesian Optimization (BO). Each of these algorithms has its own advantages and drawbacks and each offers a different approach to searching for optimal architectures.

Reinforcement Learning (RL):

Reinforcement learning is based on trial and error, where an agent learns by interacting with its environment. RL agents can explore the search space and identify potential solutions through reward-based learning.

The agent receives rewards when it makes a good decision and penalties when it makes a bad decision. This type of approach has been used to optimize recurrent neural networks, convolutional neural networks, and generative adversarial networks.

Evolutionary Algorithms (EA):

Evolutionary algorithms are inspired by biological evolution and they are based on the principles of natural selection. This method uses a population-based approach to search for the best architectures. Solutions with higher fitness values will be selected and mutated to generate new solutions in the next generation. EA has been successfully applied to optimize convolutional neural networks and recurrent neural networks.

Bayesian Optimization (BO):

Bayesian optimization is a probabilistic approach to optimize parameters and hyperparameters of a system. It iteratively updates a model that represents the function to be optimized based on past experiments.

This allows the algorithm to find better solutions more quickly than other methods. BO has been used to optimize both convolutional neural networks and recurrent neural networks.

Overall, there are many algorithms available for NAS and each algorithm has its own advantages and drawbacks. Before selecting an algorithm, one should carefully consider which approach is best suited to the specific problem at hand.

By Hari Haran

I'm Aspiring data scientist who want to know about more AI. I'm very keen in learning many sources in AI.

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