## INTRODUCTION

Linear Regression is a widely used statistical or ML method. The earliest form of regression was the method of

*least squares.*The term regression was coined by Sir Frances Galton in 1875. It was based on biological phenomenons for relating heights of descendants to their tall ancestors.Linear Regression is a type of Classification problem which best suits to Supervised learning.

**APPLICATIONS**

• Analyze the marketing effectiveness, pricing, and promotions on the sales of a product.

• Forecast sales by analyzing the monthly company’s sales for the past few years.

• Predict house prices with an increase in the sizes of houses.

• Calculate causal relationships between parameters in biological systems.

**NOTE**

**:***With more features, we do not have a line, instead, we have a plane. In higher dimensions where we have more than one input (X), the line is called a plane or a hyper-plane,*The equation can be generalized from simple linear regression to multiple linear regression as follows: Y(X)=p0 +p1 *X1 +p2 *X2 +...+pn *Xn

**SOME IMPORTANT TERMS**

**.**

*: It gives the difference between observed values and fitted values provided by a model. To get the best-fitted line in linear regression, we attempt to minimize the vertical distance between all data points and their distance to the fitted line.*

**Residuals****: It is an error from wrong assumptions in the learning algorithms. High bias can cause an algo. to miss relevant relations between features and target output.**

*.Bias***: It is an error from sensitivity to small fluctuations in the training set. High variance can cause an algo. to make random noise in training data.**

*.Variance*.

**: For any model, it is a level of complexity at which an increase in bias is equivalent to the reduction in variance if complexity exceeds sweet spot, we are in effect of over-fitting the model & if complexity falls short of the sweet spot we are under-fitting the model.***Sweet spot***LINEAR REGRESSION WITH PYTHON**

**1)**Import the necessary libraries, i.e ;

- import pandas as pd
- import numpy as np
- import matplotlib.pyplot as plt
- import seaborn as sns

*for importing datasets :*

- from sklearn import datasets

**2)**Separate dataset into two arrays, i.e

**, named as selected features and target values respectively.**

*X & y***3)**Now split the data into training sets and testing sets, i.e, X_train, X_test, y_train, y_test.

Sklearn already has method train_test_split, to do this task, so it is imported as a part of the model selection as :

- from sklearn.model_selection import train_test_split .

**4)**Now we need a linear regression model to train on our dataset, for that we import linear_model as :

- from sklearn import linear_model

# Linear regression is a part of the linear_model family.

**5)**An instance of the Linear regression model is created and stored in a variable say

**.**

*lm*- lm=linear_model.LinearRegression()

**6)**Now fit the model for train_set as :

- lm.fit( X_train , y_train )

**7)**Now to make predictions we use test_set & store in a variable for ease of future evaluation .

- pred=lm.predict( X_test)

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