least squares

• How to Compute SSreg and SSres in Regression
  Compute regression and residual sums of squares from observed and fitted values, check the total-sum-of-squares identity, and interpret R-squared.
• How to Write Least Squares in Matrix Form
  Express least squares as minimizing the residual norm ||Ax − b||, derive the normal equations, and see a fully worked linear-fit example.
• How to Minimize a Sum-of-Squares Error Function
  Minimize a sum-of-squares error by setting its gradient to zero; for linear models, solve the least-squares equations and check uniqueness.