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math415 midterm 3 sp19
uiuc math415
27
Mathematics
Undergraduate 4
04/16/2019

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Term
Incidence matrix
Definition
Dimension: m edges x n nodes

A(i,j)=

−1, if edge i leaves node j
+1 if edge i enters node j
0 otherwise
Term
Meaning of nullspace of incidence matrix
Definition
dim(Nul(A)) is number of connected subgraphs
Term
Meaning of left nullspace of incidence matrix
Definition
left nullspace = null(A^T)

dim(Nul(A^T)) is # of independent loops
Term
Orthogonal basis definition
Definition
If the vectors are orthogonal to each other.
Term
Orthogonal projection of vector x ONTO vector y
Definition
[image]
Term
Projection Matrix
Definition
Used to project x into y by using Px

Find using: [image]
Term
Orthogonal projection of x onto W
Definition
Determined by xHat

[image]

Once xˆ is determined, x⊥ (error term) = x − xˆ.
Term
Projection matrix P for orthogonal projectino onto W in R^n (or other basis)
Definition
Use columns as matrix.

Each column is following the formula:

[image]

where x is in the non W basis (1,0,0) (0,1,0), (0,0,1) for the std basis R^3
Term
P^2 (projection matrix)
Definition
P
Term
Closest point to x in span(v1,v2,..)
Definition
Follow this formula. Resulting vector/pt is closest)

[image]
Term
Find least squares solution to Ax = b (and define meaning of soln)
Definition
Solve [image]

[image] is minimal
Term
Projection matrix for proj onto Col(A)
Definition
[image]
Term
Fitting lines
Definition
Solve for beta:

[image]

where:

[image]

[image]

[image]

Line is [image]
Term
Definition
x dot y (dot product)
Term
Given a basis a1, . . . , an, produce a orthogonal basis b1, . . . , bn and an orthonormal basis q1, . . . , qn.
Definition
[image]
Term
The columns of Q are orthonormal means ___
Definition
Q^T Q = Identity
Term
orthogonal matrix
Definition
square matrix with orthonormal columns
Term
Gram Schmidt A = QR decomp
Definition
1) Gram-Schmidt on columns of A to get columns of Q
2) R = Q^T*A

Q is orthonormal, R is upper triangular
Term
Least square solution using QR decomp (Ax = b)
Definition
Find QR decomp.

Rx = Q^T b, x will be best sol'n
Term
Matrix [image]
Definition
Used for relating coordinate vectors of different basis.

[image]
Term
det(A^-1)
Definition
1/det(A)
Term
Determinant of matrix (non std way)
Definition
1) Get into upper triangular matrix
2) multiply diagonal
Term
Solve for eigenvalues (λ) of matrix A
Definition
det(A - λ * Identity) = 0
Term
Eigenvalue problem
Definition
Ax = λx (x is a eigenvector, λ is eigen value)
Term
Product of eigenvalues is
Definition
the determinant of A
Term
Trace of matrix
Definition
Sum of eigenvalues
Term
det(2) in n x n matrix
Definition
2^n
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