Machine Learning
Interview Questions
Generative and Discriminative Models

# What is the difference between a generative and discriminative model?

Generative and discriminative models are two common types of models in machine learning. The main difference between them lies in their approach to modeling the data.

A generative model learns the joint probability distribution p(x,y) of the input x and output y. In other words, it models the underlying probability distribution of the data and can generate new data points that are similar to the training data. Generative models can be used for tasks such as image and speech recognition, natural language processing, and anomaly detection.

An example of a generative model is a Gaussian mixture model (GMM) that learns the probability distribution of the input data and can generate new samples from that distribution. Another example is a generative adversarial network (GAN), which uses two neural networks to generate new data that is similar to the training data.

On the other hand, a discriminative model learns the conditional probability distribution $p(y|x)$ of the output y given the input x. In other words, it models the decision boundary between the different classes in the data. Discriminative models are commonly used for tasks such as classification, regression, and ranking.

An example of a discriminative model is logistic regression that learns the probability of a binary output based on the input features. Another example is a support vector machine (SVM) that finds the optimal decision boundary between the different classes in the data.

The choice between a generative and discriminative model depends on the task at hand. Generative models are useful when we want to generate new data that is similar to the training data, while discriminative models are useful when we want to make predictions on new data.

Pros of generative models:

• Can generate new data points that are similar to the training data
• Can be used for unsupervised learning tasks
• Can be used for anomaly detection

Cons of generative models:

• Can be computationally expensive
• May not perform as well as discriminative models for some tasks

Pros of discriminative models:

• Often have higher accuracy for classification tasks
• Typically simpler and more computationally efficient than generative models

Cons of Discriminative Models:

• Cannot generate new data points
• May not perform well in low-dimensional spaces

In summary, both generative and discriminative models have their own advantages and disadvantages, and the choice between them depends on the specific task and the available data.