Supervised learning and unsupervised learning


This article explains about basic Machine Learning concepts of Supervised learning and Unsupervised learnings. 




Human learning happens with external sense objects. You can now read English because you have learned English, but if some text is in a language which you don’t know you cannot understand it. Same applies to data driven algorithms which utilizes the data to judge are loosely called Machine Learning algorithms.

Let’s say, you want to develop Machine Learning algorithm to detect whether car exists in a image

Supervised learning

In supervised learning you'll label several images of cars and non-cars and an algorithm will eventually learn and be able to predict whether or not an unseen image has a car in it. For supervised learning the feeded data must be labeled, or explicitly mention which ones are cars and which ones aren't.




When you complete a Captcha and identify the images that have cars, you’re labeling images! A supervised machine learning algorithm can now use those pictures that you’ve tagged to make it’s car-image predictor more accurate.

Mathematical definition

In the supervised learning paradigm, the goal is to infer a function f : X → Y , the classifier, from a sample data or training set An composed of pairs of (input, output) points, xi belonging to some feature set X , and yi ∈ Y :

An = ((x1,y1),...,(xn,yn)) ∈ (X ×Y )n.

Typically X ⊂ IRd , and yi ∈ IR for regression problems, and yi is discrete for classification problems. We will often use examples with yi ∈ {−1, +1} for binary classification.
Unsupervised learning

In an unsupervised algorithm your example images are not labeled, i.e. you don't say anything. Of course, in such a case the algorithm itself cannot "invent" what a car is, but it can try to cluster the data into different groups, e.g. it can distinguish that cars are very different from animals.




References:

https://link.springer.com/chapter/10.1007/978-3-540-75171-7_2

https://www.researchgate.net/publication/342121950_What_is_Unsupervised_Learning/link/5ee30fbe299bf1faac4e78f1/download

https://www.codecademy.com/article/machine-learning-supervised-vs-unsupervised

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