# #19 Machine Learning Specialization [Course 1, Week 1, Lesson 4] | Summary and Q&A

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December 1, 2022
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DeepLearningAI
#19 Machine Learning Specialization [Course 1, Week 1, Lesson 4]

## TL;DR

Learn how to use the squared error cost function and gradient descent algorithm to train a linear regression model.

## Key Insights

• 🚂 The linear regression model can be trained by combining the squared error cost function and the gradient descent algorithm.
• 🔙 Calculating the derivatives of the cost function's parameters (W and B) using calculus helps update these parameters effectively.
• ⚾ The gradient descent algorithm iteratively adjusts the parameters based on the derivatives, gradually minimizing the cost function.
• 🌐 Using a squared error cost function with linear regression ensures a convex function, guaranteeing a single global minimum.

## Transcript

so previously you took a look at the linear regression model and then the cost function and then the gradient descents algorithm in this video we're going to put it all together and use the squared error cost function for the linear regression model with gradient descent this will allow us to train the linear regression model to fit a straight line... Read More

### Q: What is the purpose of using the squared error cost function in linear regression?

The squared error cost function measures the difference between the predicted and actual values, allowing us to quantify the model's performance and optimize it through gradient descent.

### Q: How are the derivatives for the cost function's parameters calculated?

The derivative with respect to W is obtained by calculating the sum of the error terms (predicted - actual values) multiplied by the corresponding input feature. The derivative with respect to B is similar, but does not include the input feature term.

### Q: Does understanding the calculus derivation of the derivatives matter for implementing gradient descent?

No, it is not necessary. The video provides the derived formulas, and if you don't remember calculus or aren't interested in it, you can still implement gradient descent successfully.

### Q: Why is it important to use an appropriate learning rate in gradient descent?

The learning rate determines the step size in updating the parameters. If the learning rate is too large, it may overshoot the global minimum of the cost function, while a too small learning rate may lead to slow convergence.

## Summary & Key Takeaways

• This video explains how to combine the linear regression model, squared error cost function, and gradient descent algorithm to fit a straight line to trading data.

• The derivatives for the cost function with respect to the model's parameters (W and B) are derived using calculus.

• The gradient descent algorithm is then implemented using these derivatives to update the model's parameters iteratively until convergence.