signalProcessing.jl

randChi²(df::Int)

alias: randχ²

Generate a random variable distributed as a chi-squared with df degrees of freedom.

It uses the Wilson–Hilferty transformation for df>=20 - see chi-squared distribution.

Examples

using Plots, PosDefManifold
chi=[randχ²(2) for i=1:10000]
histogram(chi) # needs Plots package. Check your plots back-end.

    randEigvals(n::Int;
    <
    df::Int=2,
    eigvalsSNR::Real=10e3 >)

alias: randλ

Generate an $n$-vector of random real positive eigenvalues. The eigenvalues are generated as in function randΛ(randEigvalsMat), the syntax of which is used.

See also: randU (randUnitaryMat), randP (randPosDefMat).

Examples

using Plots, PosDefManifold
λ=sort(randλ(10), rev=true)
σ=sort(randλ(10, eigvalsSNR=10), rev=true)
plot(λ) # needs Plots package. Check your plots back-end.
plot!(σ) # needs Plots package. Check your plots back-end.

    (1) randEigvalsMat(n::Int;
    <
    df::Int=2,
    eigvalsSNR::Real=10e3 >)

    (2) randEigvalsMat(n::Int, k::Int;
    < same keyword arguments as in (1) >)

alias: randΛ

(1) Generate an $n⋅n$ diagonal matrix of random real positive eigenvalues.

(2) An array 1d (of 𝔻Vector type) of $k$ matrices of the kind in (1)

The eigenvalues are generated according to model

$λ_i=χ_{df}^2+η,\hspace{6pt}\textrm{for}\hspace{2pt}i=1:n,$

where

• $χ_{df}^2$ (signal term) is randomly distributed as a chi-square with df degrees of freedom,
• $η$ is a white noise term, function of <keyword argument>eigvalsSNR, such that

$\textrm{eigenvalues SNR}=\mathbb{E}\big(\sum_{i=1}^{n}λ_i\big)\big/nη.$

The expected sum $\mathbb{E}\big(\sum_{i=1}^{n}λ_i\big)$ here above is the expected variance of the signal term, i.e., $n(df)$, since the expectation of a random chi-squared variable is equal to its degrees of freedom.

If eigvalsSNR=Inf is passed as argument, then $η$ is set to zero, i.e., no white noise is added. In any case eigvalsSNR must be positive.

Note that with the default value of <keyword argument>df (df=2) the generating model assumes that the eigenvalues have exponentially decaying variance, which is often observed on real data.

This function is used by function randP (randPosDefMat) to generate random positive definite matrices with added white noise in order to emulate eigenvalues observed in real data and to improve the conditioning of the generated matrices with respect to inversion.

See also: randλ (randEigvals), randU (randUnitaryMat), randP (randPosDefMat), randχ² (randChi²).

Examples

using PosDefManifold
# (1)
n=3;
U=randU(n);
Λ=randΛ(n, eigvalsSNR=100)
P=U*Λ*U' # generate an SPD matrix
using LinearAlgebra
Q=ℍ(U*Λ*U') # generate an SPD matrix and flag it as 'Hermitian'

# (2) generate an array of 10 matrices of simulated eigenvalues
Dvec=randΛ(n, 10)

(1) randUnitaryMat(n::Int)
(2) randUnitaryMat(::Type{Complex{T}}, n::Int)

aliases: randOrthMat, randU

Generate a random $n⋅n$

• (1) orthogonal matrix (real)
• (2) unitary matrix (complex)

The matrices are generated running the modified (stabilized) Gram-Schmidt orthogonalization procedure (mgs) on an $n⋅n$ matrix filled with random Gaussian elements.

See also: randΛ (randEigvals), randP (randPosDefMat).

Examples

using PosDefManifold
n=3;
X=randU(n)*sqrt(randΛ(n))*randU(n)'  # (1) generate a random square real matrix

U=randU(ComplexF64, n);
V=randU(ComplexF64, n);
Y=U*sqrt(randΛ(n))*V' # (2) generate a random square complex matrix

    (1) randPosDefMat(n::Int;
    <
    df::Int=2,
    eigvalsSNR::Real=10e3 >)

    (2) randPosDefMat(::Type{Complex{T}}, n:: Int;
    < same keyword arguments as in (1) >)

    (3) randPosDefMat(n::Int, k::Int;
    <
    df::Int=2,
    eigvalsSNR::Real=10e3,
    SNR::Real=100,
    commuting=false >)

    (4) randPosDefMat(::Type{Complex{T}}, n::Int, k::Int;
    < same keyword arguments as in (3) >)

alias: randP

Generate

• (1) one random Hermitian positive definite matrix (real) of size $n⋅n$
• (2) one random Hermitian positive definite matrix (complex) of size $n⋅n$
• (3) an array 1d (of ℍVector type) of $k$ matrices of the kind in (1)
• (4) an array 1d (of ℍVector type) of $k$ matrices of the kind in (2).

Methods (3) and (4) are multi-threaded. See Threads.

For (1) and (2) the matrix is generated according to model

$UΛU^H+ηI$,

where $U$ is a random orthogonal (1) or unitary (2) matrix generated by function randU(randUnitaryMat) and $Λ$, $η$ are a positive definite diagonal matrix and a non-negative scalar depending on <optional keywords arguments>df and eigvalsSNR randomly generated calling function randΛ(randEigvalsMat).

For (3) and (4), if the <optional keyword argument>commuting=true is passed, the $k$ matrices are generated according to model

$UΛ_iU^H+ηI,\hspace{8pt}$, for $i$=1:$k$

otherwise they are generated according to model

$(UΛ_iU^H+ηI)+φ(V_iΔ_iV_i^H+ηI),\hspace{8pt}$, for $i$=1:$k$ Eq.[1]

where

• $U$ and the $V_i$ are random (3) orthogonal/(4) unitary matrices,
• $Λ_i$ and $Δ_i$ are positive definite diagonal matrices
• $η$ is a non-negative scalar.

All variables here above are randomly generated as in (1) and (2)

• $φ$ is adjusted so as to obtain a desired output SNR (signal-to-noise ratio), which is also an

<optional keywords arguments>, such as

$SNR=\frac{\displaystyle\sum_{i=1}^{k}\textrm{tr}(UΛ_iU^H+ηI)}{\displaystyle\sum_{i=1}^{k}\textrm{tr}φ(V_iΔ_iV_i^H+ηI)}$.

A slightly different version of this model for generating positive definite matrices has been proposed in (Congedo et al., 2017b)[🎓]; in the model of Eq. [1]

• $UΛ_iU^H$ is the signal term, where the signal is supposed sharing the same coordinates for all matrices,
• $φ(V_iΔ_iV_i^H)$ is a structured noise term, which is different for all matrices
• $ηI$ is a white noise term, with same variance for all matrices.

See also: the aforementioned paper and randΛ (randEigvalsMat).

Examples

using PosDefManifold
R=randP(10, df=10, eigvalsSNR=1000) # 1 SDP Matrix of size 10x10 #(1)
H=randP(ComplexF64, 5, eigvalsSNR=10) # 1 Hermitian Matrix of size 5x5 # (2)
ℛ=randP(10, 1000, eigvalsSNR=100) # 1000 SPD Matrices of size 10x10 # (3)
using Plots
heatmap(Matrix(ℛ[1]), yflip=true, c=:bluesreds)
ℋ=randP(ComplexF64, 20, 1000) # 1000 Hermitian Matrices of size 20x20 # (4)

(1) regularize!(P::ℍ; <SNR=10e3>)
(2) regularize!(𝐏::ℍVector; <SNR=10e3>)

Add white noise to either

• (1) a positive definite matrix $P$ of size $n⋅n$, or
• (2) a 1d array $𝐏$ of $k$ positive definite matrices of size $n⋅n$, of ℍVector type.

The added noise improves the matrix conditioning with respect to inversion. This is used to avoid numerical errors when decomposing these matrices or when evaluating some functions of their eigevalues such as the log.

A constant value is added to all diagonal elements of (1) $P$ or (2) af all matrices in $𝐏$, that is, on output:

$\textrm{(1)}\hspace{2pt}P\leftarrow P+ηI$

$\textrm{(2)}\hspace{2pt}𝐏_i\leftarrow 𝐏_i+ηI, \hspace{2pt}\textrm{for}\hspace{2pt} i=1:k.$

The amount of added noise $η$ is determined by the SNR<keyword argument>, which by default is 10000. This is such that

$\textrm{(1)}\hspace{2pt}SNR=\frac{\displaystyle\textrm{tr}(P)}{\displaystyle\textrm{tr}(ηI)}.$

$\textrm{(2)}\hspace{2pt}SNR=\frac{\displaystyle\sum_{i=1}^{k}\textrm{tr}(𝐏_i)}{\displaystyle k\hspace{1pt}\textrm{tr}(ηI)}.$

$P$ in (1) must be flagged as Hermitian. See typecasting matrices.

See also: randP (randPosDefMat).

Examples

# (1)
using LinearAlgebra, Plots, PosDefManifold
n=3
U=randU(n)
# in Q we will write two matrices,
# the unregularized and regularized matrix side by side
Q=Matrix{Float64}(undef, n, n*2)
P=ℍ(U*Diagonal(randn(n).^2)*U') # generate a real 3x3 positive matrix
for i=1:n, j=1:n Q[i, j]=P[i, j] end
regularize!(P, SNR=5)
for i=1:n, j=1:n Q[i, j+n]=P[i, j] end # the regularized matrix is on the right
heatmap(Matrix(Q), yflip=true, c=:bluesreds)

# (2)
𝐏=[ℍ(U*Diagonal(randn(3).^2)*U') for i=1:5] # 5 real 3x3 positive matrices
regularize!(𝐏, SNR=1000)

Run a test

using LinearAlgebra
𝐏=randP(10, 100, SNR=1000); # 100 real Hermitian matrices
signalVar=sum(tr(P) for P in 𝐏);
regularize!(𝐏, SNR=1000);
signalPlusNoiseVar=sum(tr(P) for P in 𝐏);
output_snr=signalVar/(signalPlusNoiseVar-signalVar)
# output_snr should be approx. equal to 1000

gram(X::Matrix{T}) where T<:RealOrComplex

Given a generic data matrix $X$, comprised of real or complex elements, return the normalized Gram matrix, that is, the covariance matrix of $X$ corrected by sample size, but without subtracting the mean.

The result is flagged as Hermitian. See typecasting matrices.

Examples

using PosDefManifold
X=randn(5, 150);
G=gram(X) # => G=X*X'/150
X=randn(100, 2);
F=gram(X); # => G=X'*X/100

trade(P::ℍ{T}) where T<:RealOrComplex

Given a positive definite matrix P, return as a 2-tuple the trace and the determinant of P. This is used to plot positive matrices in two dimensions (TraDe plots: log(trace/n) vs. log(determinant), see exemple here below).

P must be flagged by julia as Hermitian. See typecasting matrices.

Examples

using PosDefManifold
P=randP(3)
t, d=trade(P)  # equivalent to (t, d)=trade(P)

# TraDe plot
using Plots
k=100
n=10
𝐏=randP(n, k, SNR=1000); # 100 real Hermitian matrices
x=Vector{Float64}(undef, k)
y=Vector{Float64}(undef, k)
for i=1:k
    x[i], y[i] = trade(𝐏[i])
end
x=log.(x./n)
y=log.(y)
plot(x, y, seriestype=:scatter)