Logistic regression (for classification)

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• Email: spam or not spam
• Tumor: malignant or benign
• Online Transaction: Fraudlent or not?

Binary classification:

y can be either 0 or 1,

• 0 = Negative class
• 1 = Positive class

Multi-class classification problem when y can have more than 2 distinct values

• Linear regression using a threshold value

• Sigmoid function / Logistic function
• Decision boundary

• The "Logistic regression cost function" based on the Sigmoid function is a non-convex function so Gradient Descent isn't guarnteed to reach global minimum. So intead of that we use some log() function.

Optimization algorithms

• Gradient descent
• Conjugate gradient
• BFGS
• L-BFGS

The other 3 algorthms have the advantage of not needing to pick a alfa (learning pace), and they are often faster than Gradient descent. However they are more complex to implement.