Regression and Classifications are two major area in Classification Technique in Data Mining.

Toady I heared a question what is regression and what is classification and where am i use which condition.

The Image says lots of word than I write.

The key point is if you have large data and you want to :

- Find the Catagories of that You shoud follow the path via classification.
- You want to know the quantity you have to follow the path from regression.

**Regression** : Is the task when the dicrete output y consist of one or more __continuos variables.__

**Classification** : Is the task when the dicrete output y consist of one or more __dicrete varaibles.__

Let’s consider a input vector X1,X2,X3,…….. Xn and output vector varaible Y respresenting the class varaibles Y1,Y2,Y3,…..Yn, Where n is the number of training sample.

We can express these as in mathematical function below

**f(x) = y(x,w)** ,where w is some adjustable parameters.

A classifier can view as the overall system that maps from X to Y.

Training is the process of __finding the values for adjustable parameter__ **w** of the mapping function **f** on basis of the dataset. That dataset is refered as **training set.**

Testing preformance of a classifier is known as generalisation.

If training performance > testing performance is called **overfit**.

One way to **reduce the overfit** is **divide the training data** into **training & validation subsets.**

A well known training testing protocol for this is **n-fold cross validation**.

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