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Master hyperparameter tuning for machine learning models

March 28, 2023

Machine learning algorithms require the use of various parameters that govern the learning process. These parameters are called hyperparameters, and their optimal values are often unknown a priori. Hyperparameter tuning is the process of selecting the best values of these parameters to improve the performance of a model. In this article, we will explore the basics of hyperparameter tuning and the popular strategies used to accomplish it.  

Understanding hyperparameters 

In machine learning, a model has two types of parameters: Hyperparameters and learned parameters. The learned parameters are updated during the training process, while the hyperparameters are set before the training begins.

Hyperparameters control the model’s behavior, and their values are usually set based on domain knowledge or heuristics. Examples of hyperparameters include learning rate, regularization coefficient, batch size, and the number of hidden layers.

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Why is hyperparameter tuning important? 

The values of hyperparameters significantly affect the performance of a model. Suboptimal values can result in poor performance or overfitting, while optimal values can lead to better generalization and improved accuracy. In summary, hyperparameter tuning is crucial to maximizing the performance of a model. 

Hyperparameter tuning for ML models
Hyperparameter tuning for ML models

Strategies for hyperparameter tuning 

There are different strategies used for hyperparameter tuning, and some of the most popular ones are grid search and randomized search. 

Grid search: This strategy evaluates a range of hyperparameter values by exhaustively searching through all possible combinations of parameter values in a grid. The best combination is selected based on the model’s performance metrics.  

Randomized Search: This strategy evaluates a random set of hyperparameter values within a given range. This approach can be faster than grid search and can still produce good results. 

H3: general hyperparameter tuning strategy 

To effectively tune hyperparameters, it is crucial to follow a general strategy. According to, a general hyperparameter tuning strategy consists of three phases: 

  • Preprocessing and feature engineering 
  • Initial modeling and hyperparameter selection 
  • Refining hyperparameters 


Preprocessing and feature engineering
 

The first phase involves preprocessing and feature engineering. This includes data cleaning, data normalization, and feature selection. In this phase, hyperparameters that affect the preprocessing and feature engineering steps are set, such as the number of features to be selected. 

Initial modeling and hyperparameter selection 

The second phase involves initializing the model and selecting a range of hyperparameter values to test. This includes setting the model type and other model-specific hyperparameters, such as the learning rate or the number of hidden layers.  

Refining hyperparameters 

In the final phase, the hyperparameters are fine-tuned by adjusting their values based on the model’s performance metrics. This can be done using gridsearchcv, randomizedsearchcv, or other strategies. 

Most common questions asked about hyperparameters 

Q: Can hyperparameters be learned during training? 

A: No, hyperparameters are set before the training begins and are not updated during the training process.   

Q: Why is it necessary to set the hyperparameters? 

A: Hyperparameters control the learning process of a model, and their values can significantly affect its performance. Setting the hyperparameters helps to improve the model’s accuracy and prevent overfitting. 

Methods for hyperparameter tuning in machine learning

Hyperparameter tuning is an essential step in machine learning to fine-tune models and improve their performance. Several methods are used to tune hyperparameters, including grid search, random search, and bayesian optimization. Here’s a brief overview of each method:  

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1. Grid search:

Grid search is a commonly used method for hyperparameter tuning. In this method, a predefined set of hyperparameters is defined, and each combination of hyperparameters is tried to find the best set of values.

Grid search is suitable for small and quick searches of hyperparameter values that are known to perform well generally. However, it may not be an efficient method when the search space is large. 

2. Random search:

Unlike grid search, in a random search, only a part of the parameter values are tried out. In this method, the parameter values are sampled from a given list or specified distribution, and the number of parameter settings that are sampled is given by n_iter.

Random search is appropriate for discovering new hyperparameter values or new combinations of hyperparameters, often resulting in better performance, although it may take more time to complete. 

3. Bayesian optimization:

Bayesian optimization is a method for hyperparameter tuning that aims to find the best set of hyperparameters by building a probabilistic model of the objective function and then searching for the optimal values. This method is suitable when the search space is large and complex.

Bayesian optimization is based on the principle of Bayes’s theorem, which allows the algorithm to update its belief about the objective function as it evaluates more hyperparameters. This method can converge quickly and may result in better performance than grid search and random search.

Choosing the right method for hyperparameter tuning

In conclusion, hyperparameter tuning is essential in machine learning, and several methods can be used to fine-tune models. Grid search is a simple and efficient method for small search spaces, while the random search can be used for discovering new hyperparameter values.

Bayesian optimization is a powerful method for complex and large search spaces that can result in better performance by building a probabilistic model of the objective function. It’s choosing the right method based on the problem at hand is essential. 

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