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Linear Least Squares Problems
Orthogonalization methods; SVD
15
Computer Science
Graduate
03/02/2014

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Cards

Term
Orthogonality
Definition

matrix -- ATA = AAT = I

two vectors -- <u,v> = 0

functions -- ∫f(x)g(x)dx = 0

Term
Idempotence
Definition
P = P2
Term
Orthogonal Projector
Definition
Idempotent and Orthogonal Matrix
Term
Existence/Uniqueness of Least Squares Solutions
Definition
Always exist.  Unique when A is not rank deficient.
Term
Normal Equations
Definition
ATAx = ATb where ATA is an mxm matrix.  Can solve with LU factorization.
Term
Householder Reflections
Definition

Ha = a - 2(vTa/vTv)v

v = a - alpha(ek)

alpha = -sign(ak)||ak|| where ais a vector from position k on

Term
Givens Rotations
Definition
[image]
Term
QR Factorization
Definition

Orthogonal transformation to triangular form A=QR

[image]

Term
Classical Gram-Schmidt
Definition

Orthogonalize each successive vector against all the preceding ones.

[image]

Term
Modified Gram-Schmidt
Definition

As soon as each new vector qk is computed, immediately orthogonalize all remaining vectors against it... can use column pivoting

[image]

Term
Euclidean Norm & SVD
Definition
||A||2 = σmax
Term
Condition Number and SVD
Definition
cond(A) = σmax/σmin
Term
Rank and SVD
Definition
The rank of a matrix is equal to the number of nonzero singular values that it has
Term
Pseudoinverse and SVD
Definition
A+ = VΣ+UT where the pseudo inverse of a scalar σ is 1/σ.
Term
Orthonormal Bases and SVD
Definition
The columns of U corresponding to nonzero singular values form an orthonoral basis for span(A) and remaining columns of U form orthonoral basis for its orthogonal complement.  Columns of V corresponding to zero singular values form orthonormal basis for null space of A, and remaining columns of V form orthonormal basis for orthogonal complement of null space.
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