01_Introducation/Categorys/Cost Function/

introducation

What’s Machine Learning?

• Arthur Samuel: “the field of study that gives computers the ability to learn without being explicitly programmed.”
• Tom Mitchell: “A computer program is said to learn from experience E with respect to some class of tasks T and performance measure P, if its performance at tasks in T, as measured by P, improves with experience E.”

Two Typical Category

Supervised Learning

Every example has its label

• Regression problem
• Classification problem

Unsupervised Learning

haven’t given the label of example

• structure learning
• clustering

Model and Cost Function

Model Representation

choose a type of model and use an algorithm to find the optimal parameters

Cost Function

using a cost function, the accuracy of hypothesis function can be measured.

The most common Cost Function is the Squared Error Function or Mean squared error

Linear Regression with one variable

Hypothesis:
Parameters:
Cost Function:
Goal：