## 1. Introduction

In this tutorial, we’ll talk about two popular machine learning categories, flexible and inflexible models. First, we’ll briefly introduce the term model flexibility and then get deeper into flexible and inflexible models**. **Next, **we’ll analyze reasons for employing models for each category and talk about the most common models of each category**. We’ll also discuss the benefits and limitations of each category and talk about their main differences.

## 2. What Is Model Flexibility?

**Model flexibility denotes a model’s capacity to adapt, evolve, and learn from data input**. Generally, model flexibility can vary, and different models may have different levels of flexibility. Therefore, it is an essential concern as it can impact a model’s accuracy, efficiency, and generalizability.

## 3. Flexible Models

**Flexible models are those that can adapt and learn from data and can make predictions or decisions based on a wide range of inputs**. These models are able to capture complex patterns and relationships in data and can generalize well to new, unseen data. Usually, they require large amounts of data and computation to be trained than inflexible models, but they are able to provide higher accuracy performance and generalizability than inflexible models. This can make them valuable in a wide range of machine-learning applications.

A flexible model may be employed in machine learning for a variety of purposes, including:

### 3.1. Accuracy and Performance

Flexible models are frequently more reliable and increase the overall performance than inflexible models. This is due to their ability to adapt and learn from information as well as catch sophisticated patterns and correlations that an inflexible model may not be able to detect.

### 3.2. Generalizability

Flexible models are frequently more broadly applicable than inflexible models. This implies they may generate accurate estimations or conclusions based on previously unseen information and are not constrained by the assumptions and restrictions of an inflexible model.

### 3.3. Scalability

Flexible models are usually scalable, meaning they can handle enormous amounts of data and can be trained in a parallel way on distributed systems. Distributed processing and parallel computing are advantageous when the input data is huge and complex, as they shorten the time for training.

### 3.4. Ability to Learn

Flexible models usually adapt based on their input data. Therefore, they result in improving their accuracy and effectiveness over time. So this can be beneficial in applications where the data is dynamic and shifting all the time, and a model needs to adjust to these changes.

## 4. Examples of Flexible Models

Some examples of flexible models in machine learning include:

### 4.1. Neural Networks

**Neural networks are flexible models constructed of several layers of weighted connections or neurons**. They may adapt to understand and categorize complicated data by employing techniques like backpropagation. Classification of images, audio recognition, and natural language processing are all common applications for neural networks.

### 4.2. Decision Trees

**Decision trees are a form of flexible model that generates predictions or judgments using a tree-like architecture**. The tree’s nodes reflect decisions or conditions, while the branches indicate likely results. Decision trees, which can adjust and expand to new information, are taught using algorithms such as ID3. They are frequently applied to classification and regression problems.

### 4.3. Support Vector Machines

**Support vector machines are a sort of flexible model that separates different types of data using a hyperplane**. They are trained to optimize the distance between distinct classes by employing methods such as the SMO method. SVMs are frequently utilized for classification, regression, and fault diagnosis.

## 5. Inflexible Models

Inflexible models, on the other hand, are solid and unable to adjust to unseen data. **Therefore models of this category can’t adapt or learn from data and make predictions or conclusions based on a predefined set of assumptions and rules**. Moreover, while inflexible models are less accurate and generalizable than flexible models, they can nevertheless be beneficial and give significant insights and forecasts in situations where simplicity, interpretability, and speed are the desirable aspects of the model.

An inflexible model may be employed in machine learning for a variety of reasons, including:

### 5.1. Simplicity and Interpretability

Inflexible models are frequently simpler and easier to be understood by programmers than flexible models. This improves their interpretability and gives valuable insights into the underlying aspects and relationships of data.

### 5.2. Speed and Efficiency

Inflexible models are generally faster and more efficient during the training phase than flexible models. Moreover, their usage is quite simpler and can be easily evaluated and tested. This can be important in applications where time and computational resources are limited.

### 5.3. Domain Knowledge and Expertise

In circumstances where domain expertise and knowledge are accessible to establish and develop the model, inflexible models may be preferable. Such insight might result in a model that is more suited to the application’s unique objectives, aims, and requirements.

### 5.4. Data Availability and Quality

In circumstances when data is dirty, little, and of poor quality, inflexible models may be recommended. In these instances, a flexible model may be unable to learn successfully, but an inflexible model may function more effectively.

## 6. Examples of Inflexible Models

Some examples of inflexible models in machine learning include:

### 6.1. Linear Regression

**Linear regression is a tight model that is used to describe the correlation between one or even more dependent and independent variables**. Assuming that the connections of the variables are linear, linear regression generates forecasts and calculates a set of coefficients like weights. Linear regression is commonly used for regression and predicting tasks.

### 6.2. Logistic Regression

Logistic regression is a tight model that is also employed to describe the connection between one or even more dependent and independent variables. The main difference between linear and logistic regression is that the second one generates forecasts based on the assumption that the connection is logistic and calculates a set of coefficients as well. Logistic regression is mostly used for classification and probability estimates.

### 6.3. K-means

**K-means clustering is a tight model that is used to arrange points of data into larger groups**. It employs a fixed amount of clusters and allocates data points to the nearest cluster center repeatedly. K-means clustering is commonly used for cluster analysis and data segmentation.

## 7. Conclusion

In this article, we walked through model flexibility. We introduced flexible and inflexible models, mentioned their main benefits and limitations, and talked about the most common models of each category.

**In general, flexible models are more powerful and accurate than inflexible models but require more data and computation during the training phase**. Inflexible models, on the other hand, are simpler and faster to train but may not be as accurate or generalizable.