method

classifier

A machine learning model that assigns input data to predefined categories or classes.
54 related articles

Description

A classifier is a machine learning model that assigns input data to predefined categories or classes. It learns a decision boundary from labeled examples — data points with known categories — and then applies that boundary to new, unseen data. Classifiers are the workhorses of modern pattern recognition: they power spam filters, medical diagnostics, image recognition, and scientific discovery pipelines.

History

The concept emerged in the 1950s with early work on linear discriminants by R. A. Fisher and the perceptron by Frank Rosenblatt. Modern deep learning classifiers, which dominate current practice, arose from the 2010s onward with advances in neural network architectures and computing power.

How it works

The model is trained on a dataset where each example has features (e.g., pixel values, spectral peaks, gene expression levels) and a label (e.g., 'crystal' or 'not crystal'). During training, the algorithm adjusts its internal parameters to minimize the error between its predictions and the true labels. Once trained, the classifier takes new feature vectors and outputs a probability distribution over the possible classes, typically choosing the most likely one. Different algorithms — from logistic regression to deep neural networks — differ in how they represent the decision boundary and how they handle complex, high-dimensional data.

In practice

Classifiers are used everywhere: in medical imaging to distinguish tumors from healthy tissue, in materials science to identify crystal structures from diffraction patterns, and in particle physics to separate signal events from background noise.

Fun fact

A classifier trained on satellite data can distinguish cloud types and improve climate models, as described in the article 'Облачные специи: как нейросеть улучшает климатические модели'.

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