Linear Systems
Row Reduction
We row reduce a matrix by performing row operations, in order to find a simpler but
equivalent system for which the solution set is easily read off.
Notation for Row Operations
We summarize the notation to keep track of the precise row operations being
used.
Matrix Equations
Matrices and vectors can be used to rewrite systems of equations as a single equation,
and there are advantages to doing this.
Vector Spaces and Linear Transformations
Definition of a vector space
A vector space is a set equipped with two operations, vector addition and scalar
multiplication, satisfying certain properties.
Subspaces
A subset of a vector space is a subspace if it is non-empty and, using the restriction
to the subset of the sum and scalar product operations, the subset satisfies the
axioms of a vector space.
Linear combinations and linear independence
A linear combination is a sum of scalar multiples of vectors.
Spanning sets, row spaces, and column spaces
A collection of vectors spans a set if every vector in the set can be expressed
as a linear combination of the vectors in the collection. The set of rows or
columns of a matrix are spanning sets for the row and column space of the
matrix.
Bases and dimension
A basis is a collection of vectors which consists of enough vectors to span the space,
but few enough vectors that they remain linearly independent. It is the same as a
minimal spanning set.
Vector spaces over ℂ
To complete this section we extend our set of scalars from real numbers to complex
numbers.
Definition
A linear transformation is a function between vector spaces preserving the structure
of the vector spaces.
Matrix representations of transformations
A linear transformation can be represented in terms of multiplication by a
matrix.
Vector spaces of linear transformations
The collection of all linear transformations between given vector spaces itself forms a
vector space.
Eigenvalues and Eigenvectors
The Determinant
The determinant summarizes how much a linear transformation, from a vector space
to itself, “stretches” its input.
Combinatorial definition
There is also a combinatorial approach to the computation of the determinant.
Properties of the determinant
The determinant is connected to many of the key ideas in linear algebra.
Definition
A nonzero vector which is scaled by a linear transformation is an eigenvector for that
transformation.
Eigenspaces
The span of the eigenvectors associated with a fixed eigenvalue define the eigenspace
corresponding to that eigenvalue.
The characteristic polynomial
Establish algebraic criteria for determining exactly when a real number can occur as
an eigenvalue of .
Direct sum decomposition
The subspace spanned by the eigenvectors of a matrix, or a linear transformation,
can be expressed as a direct sum of eigenspaces.
Similarity and diagonalization
Similarity represents an important equivalence relation on the vector space of square
matrices of a given dimension.
Generalized eigenvectors
For an complex matrix , does not necessarily have a basis consisting of eigenvectors
of . But it will always have a basis consisting of generalized eigenvectors of
.