
Mathematica l Notation
X random variable
x realization of X, observation
X random (column) vector
x realization of X (vector observation)
X data design matrix for X
G, g, G, g, G as above, desig nating pixel gray-values
x
⊤
transposed form of the vector x (row vector)
kxk length o r (2-)norm of x
x
⊤
y inner product of two vectors (scalar)
x · y Hadamard (component-by-component) product
xy
⊤
outer product of two vectors (matrix)
C matrix
x
⊤
Cy quadratic form (scalar)
|C| determinant of C
tr(C) trace of C
I identity matrix
0 column vector of zeroes
1 column vector of ones
Λ Diag(λ
1
. . . λ
N
) (diago nal matrix of eigenva lue s)
∂f(x)
∂x
partial derivative of f (x) with resp ...