## Polynomial Regression :

Polynomial regression is a type of regression analysis in which the relationship between the independent variable x and the dependent variable y is modeled as an nth degree polynomial. Polynomial regression can be used to model relationships between variables that are not linear.

For example, let’s consider a situation where we want to predict the temperature of a city based on the altitude of the city. We can plot the altitude and temperature of different cities on a graph and we will get a curve instead of a straight line. In such a case, a linear regression model will not be able to accurately predict the temperature based on the altitude. However, a polynomial regression model can fit a curve to the data and provide more accurate predictions.

Another example is predicting the price of a house based on its size. In this case, we can use a linear regression model to predict the price of a house based on its size. However, if we plot the size and price of different houses on a graph, we will see that the relationship is not linear. A polynomial regression model can fit a curve to the data and provide more accurate predictions.

In general, polynomial regression models are used to model relationships between variables that are not linear. These models can be fit using the same techniques as linear regression, but the relationship between the independent and dependent variables is modeled using a polynomial equation instead of a straight line.

There are several different types of polynomial regression, including linear, quadratic, cubic, and higher order polynomial regression. Linear polynomial regression models the relationship between the independent and dependent variables as a straight line. Quadratic polynomial regression models the relationship as a parabola. Cubic polynomial regression models the relationship as a cubic curve. Higher order polynomial regression models the relationship using a polynomial with a degree higher than 3.

To fit a polynomial regression model, we can use the same techniques as linear regression. First, we need to select the degree of the polynomial that best fits the data. This can be done by comparing the performance of different polynomial models using techniques such as cross-validation. Once the best fitting polynomial has been selected, we can use techniques such as gradient descent to estimate the coefficients of the polynomial equation.

One of the advantages of polynomial regression is that it can model relationships between variables that are not linear. However, there are also some limitations to this approach. One of the main limitations is that polynomial regression models can be prone to overfitting, especially when the degree of the polynomial is high. Overfitting occurs when the model fits the training data too well and does not generalize well to new data. To avoid overfitting, it is important to use techniques such as cross-validation to select the degree of the polynomial and to use regularization techniques to prevent the model from fitting the noise in the data.

In conclusion, polynomial regression is a type of regression analysis in which the relationship between the independent and dependent variables is modeled using a polynomial equation. These models can be used to model relationships between variables that are not linear and can provide more accurate predictions than linear regression models in some cases. However, polynomial regression models can be prone to overfitting and it is important to use techniques such as cross-validation and regularization to prevent this from occurring.