1. Vectors

Linear Algebra



Weiqi Zhou

Vectors on

  • ordered tuple:

  • column vector:

  • row vector:

Convention

In this course vectors are by default column vectors

Transpose

  • swap rows and columns

  • example:

  • apparently

Addition



Scalar multiplication



Geometric implications

Vector space

  • a set with specific addition and scalar multiplication rules

  • a vector is an element in the vector space

  • example: polynomials

  • example: continuous functions on

Linear combinations

Given and

is a linear combination of (with coefficients )

Linear dependence

  • Given

  • if there exist , with at least one of which being non-zero, so that ,then are said to be linearly dependent

  • otherwise if holds only at ,then they are called linearly independent

Example

  • and are linearly independent



Example

  • are linearly dependent

Motivation

If , and ,

then can be written as linear combinations of other vectors:

Exercise

  • Let


  • are linearly dependent or independent?

  • how about

Exercise

  • Determine linear dependence of the two sets below respectively





Tips

  • Let be a set of vectors

  • If ,then vectors in are linearly dependent

  • If ,and ,then vectors in are linearly dependent

Exercise

  • Let


  • write into linear combinations of

Summary

  • Concepts

  • Addition and scalar multiplication

  • Linear Dependence