Common supervised learning algorithms

Supervised learning is a type of machine learning that uses labeled examples to train algorithms to predict unseen examples. The goal is to learn a function that maps input data to output labels.

In supervised learning, the algorithm receives a training data set that contains a series of input examples and their corresponding correct output labels. By using this data set, the algorithm is able to learn a function that predicts the output label for new examples. To evaluate the performance of an algorithm, we usually use an independent test data set to verify the accuracy of the learned function. This test data set is used to test the performance of the algorithm on unseen data.

1. Linear Regression

Linear regression is a method for predicting continuous values ​​that assumes a relationship between features and targets is linear. The goal is to find the best-fit line that minimizes the sum of squared errors between the predicted value and the true value. Additionally, linear regression can be used with polynomial regression to fit a polynomial curve to the data.

2. Logistic Regression

Logistic regression is an algorithm used for binary classification. It is a regression algorithm because it predicts continuous values, but it is often used in classification tasks because it uses a logistic function to convert predicted values ​​into probabilities. Logistic regression is called "logistic" regression because it uses the logistic function (also called the sigmoid function) to predict the probability that a sample belongs to a certain class.

Its goal is to use an optimization algorithm (such as gradient descent) to learn a set of weights that can be used to predict the probability that a sample belongs to a specific class. Predictions are made by thresholding the predicted probabilities.

3. Support Vector Machine (SVM)

The support vector machine algorithm is a linear classifier that tries to find A hyperplane that maximally separates two classes for classification and regression.

SVM works by learning a set of weights that define a hyperplane. The hyperplane is chosen such that it maximizes the separation of classes and has the maximum distance (called margin) to the nearest example of each class. Once the hyperplane is found, SVM can be used to classify new examples by projecting them into feature space and predicting the class based on which side of the hyperplane they fall. The kernel function can be linear or nonlinear, and it transforms the data into a higher dimensional space, allowing the support vector machine to find linear boundaries in the transformed space.

SVMs are particularly useful for tasks where the data is high-dimensional and linearly non-separable, because they can learn non-linear functions by mapping the input data into a high-dimensional space (which may be linearly separable). linear decision boundary and then learn the decision boundary in that space (also known as the kernel trick).

4. Decision tree

The decision tree algorithm is a non-linear classifier based on the tree structure used for classification and regression predict. It works by recursively dividing the input space into regions based on feature values.

Decision trees work by recursively dividing the input space into multiple regions based on feature values. At each step in the tree, the algorithm selects the features that best segment the data based on segmentation criteria such as the Gini index or information gain. The process continues until a stopping criterion is reached, such as the maximum depth of the tree or the minimum number of examples in leaf nodes.

To make predictions for new examples, the algorithm follows the branches of the tree based on feature values ​​until it reaches a leaf node. Predictions are then made based on the majority class of the examples in the leaf nodes (for classification tasks) or the mean or median of the examples in the leaf nodes (for regression tasks).

Decision tree is a simple and interpretable model, and easy to implement. They are also fast to train and predict, and can handle a variety of data types. However, decision trees can be prone to overfitting, especially when the tree is allowed to grow very deep.

5.K Nearest Neighbors (KNN)

The K nearest neighbor algorithm is a non-parametric method that is based on the Predict the majority class of K recent examples for classification and regression.

The working principle of KNN is to store all training samples and then predict based on the K samples closest to the test samples in the feature space. The value of K is a hyperparameter chosen by the practitioner. For classification, predictions are made based on the majority class of the K recent examples. For regression, predictions are made based on the mean or median of the target variable over the K recent examples.

KNN can be computationally expensive because the algorithm needs to calculate the distance between the test example and all training examples. It may also be sensitive to the choice of K and distance metric. It also serves as a baseline model for comparison with more advanced algorithms.

6. Naive Bayes

The Naive Bayes algorithm is a probabilistic classifier that, given the presence of certain features In some cases, predictions are made based on the probability of certain events occurring. Naive Bayes makes the "naive" assumption that all features in the data are independent of each other given a class label. This assumption is often unrealistic, but the algorithm works well in practice despite this assumption.

There are many variations of the Naive Bayes algorithm. Gaussian Naive Bayes is used for continuous features and assumes that the features follow a normal distribution. Polynomial Naive Bayes is used for count data and assumes that the features follow a polynomial distribution. Bernoulli Naive Bayes is used for binary features and assumes that the features follow a Bernoulli distribution. Naive Bayes is a simple and efficient algorithm that is easy to implement and fast in training and prediction.

7. Neural Network

Neural network is a machine learning algorithm inspired by the structure and function of the brain. They consist of artificial neurons connected together in layers, called nodes or units. Neural networks can learn to perform a wide range of tasks, including classification, regression, and sequence generation. They are particularly suitable for tasks that require learning complex relationships between input data and outputs.

There are many different types of neural networks, including feedforward neural networks, convolutional neural networks, and recurrent neural networks. Feedforward neural network is the most basic type of neural network, consisting of an input layer, one or more hidden layers, and an output layer. Convolutional neural networks are used for tasks such as image classification and object detection, and they are designed to process data with a grid-like structure, such as images. Recurrent neural networks are used for tasks such as language translation and speech recognition, and they are designed to process sequential data, such as time series or natural language.

Neural networks are trained using an optimization algorithm, such as stochastic gradient descent, to minimize a loss function that measures the difference between the predicted and true output. The weights of connections between nodes are adjusted during training to minimize loss.

8. Random Forest

The random forest algorithm is an ensemble method that combines the predictions of multiple decision trees to make the final prediction. Random forests are created by training many decision trees on different subsets of the training data and then averaging the predictions of the individual trees. This process is called bootstrapping because the tree is trained on bootstrap samples of the data. The bootstrapping process introduces randomness into the tree training process, which helps reduce overfitting.

Random forests are widely used for tasks such as classification, regression, and feature selection. They are known for their ability to handle large data sets with many features and for their good performance in a wide range of tasks. They are also resistant to overfitting, which makes them a good choice for many machine learning applications.

9.Boosting algorithm

Boosting is a machine learning technique that involves training a series of weak models and combining their predictions to make Make a final prediction. In boosting, weak models are trained sequentially, and each model is trained to correct the errors of the previous model. The final prediction is made by combining the predictions of individual weak models using a weighted majority vote. The weights of individual models are usually chosen based on the accuracy of the model. Boosting is commonly used for tasks such as classification and regression. It is known for its ability to achieve high accuracy on a wide range of tasks and its ability to handle large data sets with many features.

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