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Linear Algebra
Facts Sheet
29
Mathematics
Undergraduate 3
05/03/2009

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Term
det(AB)
Definition
det(A)det(B)
Term
det(AT)
Definition
det(A)
Term
A and det(A) /= 0
Definition
is invertible
Term
det(A - λI)= 0
Definition
Characteristic Equation
Term
Roots of Characteristic Equation
Definition
are the eigenvalues of A
Term
fundamental Theorem of Algebra tells us
Definition
that a polynomial of degree 'n' has at most n distinct roots
Term
homogeneous system is when
Definition
Ax = 0
Term
3 vectors, v1, v2, v3 are linearly independent provided that
Definition
the only solution to x1v2 + x2v2+ x3v3 = 0 is the trivial solution i.e. x1=x2=x3=0
Term
Span {v1, v2, v3,}
Definition
the collection of all vectors that can be written as a linear combination of v1, v2, v3.
Term
Let V be a vector space. B = {b1, b2,...bn} is a basis for V if
Definition
b1, b2, b3 are linearly independent and B spans V
Term
Subspaces V has three properties:
Definition
0 vector is in V; if a and b are in V so is a + b; if a is in V then so is ca where c is any scalar
Term
Important subspaces are:
Definition
NulA - all vectors x such that Ax = 0;
ColA - all vectors that can be written as a linear combination of the columns of A
Term
Matrix multiplication is _____ commutative
Definition
not always
Term
Linear transformation L has 3 properties:
Definition
L(0vector) = 0 vector; L(v1 + v2) = L(v1) + L(v2); L(cv1) = cL(v1)
Term
dimensions of a subspace equal
Definition
number of vectors in a basis
Term
fundamental theorem of linear algebra is:
Definition
rankA + dimNulA = n
Term
Eigenvalues are
Definition
the roots to det(A - λI) = 0
Term
Eigenvectors are from (come from)
Definition
the nullspace of (A - λI)x = 0
Term
(AB)T =
Definition
BTAT
Term
A = PDP-1 means
Definition
A is diagonalizable
Term
in equation A = PDPT columns of P are:
Definition
The eigenvectors of A
Term
A property of a diagonalizable matrix
Definition
Raising A to a power is simplified - AK = PDKP-1
Term
u • y =
Definition
uT x y
Term
A matrix U has orthonormal columns if
Definition
if and only if U^t x U = I
Term
If U has orthonormal columns then some properties of U are:
Definition

U preserves distances and dot products:

aka || Ux|| = ||x||; Ux • Uy = x • y Ux • Uy = U0vector if and only if x "dot" y = 0

Term
An orthogonal matrix has
Definition
orthonormal columns
Term
Gram - Schmidt Algorithm is
Definition

 

 

v1=x1 v2 = x2 - ((x2 • v1)/(v1  • v1)) x v1

v3 =x3-((x3 • v1)/(v1 • v1)) x v1 - (x3 • v2)/(v2 • v2) x v2

Term
projwy is
Definition

y = ((y • U1)/(U1 • U1))x U1 +......

((y • Up)/Up • Up) x Up

Term
Invertible Matrix Theorem has following properties: (either all true or all false)
Definition

1) A is invertible

2) A is row equivalent to the nxn identity matrix 3)A has n pivot positions

4)Ax=0vector has only the trivial solutions 5)columns of A are linearly independent

6)The linear transformation x to Ax is 1-to-1

7)Ax = b is always consistent

8)Columns of A span R^n

9)the linear transformation x to Ax maps R^n onto 1

10) There exists Cnxn such that CA = I

11) there exists Dnxn such that AD = I

12) AT is invertible matrix

13) det(A)/=0

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