Which of the following is NOT a type of machine learning?

Constructive Learning is not recognized as a standard category of machine learning. The primary types of machine learning include Supervised Learning, Unsupervised Learning, and Reinforcement Learning.

Supervised Learning involves training models on labeled data, allowing the machine to learn the relationship between input features and the corresponding output. This approach is commonly used in scenarios where historical data is available, enabling predictions or classifications based on new data inputs.

Unsupervised Learning, on the other hand, deals with unlabeled data. The objective here is to uncover hidden patterns or intrinsic structures within the data without explicit instructions on what to look for. Clustering and dimensionality reduction are typical techniques used in this domain.

Reinforcement Learning is a different paradigm where an agent learns to make decisions by interacting with an environment, receiving rewards or penalties based on its actions. This trial-and-error approach is widely used in areas like robotics and game playing.

While Constructive Learning may refer to various educational or developmental frameworks in different contexts, it does not fit into the conventional classification of machine learning methodologies, making it the correct answer to identify as not a type of machine learning.