Version: 0.1.1
Date: 2019-12-18
Title: Detrended Fluctuation and Detrended Cross-Correlation Analysis
Depends: R (≥ 3.5.0)
Imports: checkmate
Suggests: lattice
Description: A collection of functions to perform Detrended Fluctuation Analysis (DFA) and Detrended Cross-Correlation Analysis (DCCA). This package implements the results presented in Prass, T.S. and Pumi, G. (2019). "On the behavior of the DFA and DCCA in trend-stationary processes" <doi:10.48550/arXiv.1910.10589>.
License: GPL (≥ 3)
Encoding: UTF-8
LazyData: true
NeedsCompilation: yes
Packaged: 2019-12-19 00:11:21 UTC; Taiane
Author: Taiane Schaedler Prass ORCID iD [aut, cre], Guilherme Pumi ORCID iD [aut]
Maintainer: Taiane Schaedler Prass <taianeprass@gmail.com>
Repository: CRAN
Date/Publication: 2020-01-01 15:10:02 UTC

Expected value of the detrended variance

Description

Calculates the expected value of the detrended variance.

Usage

EF2dfa(m = 3, nu = 0, G, K = NULL)

Arguments

m

an integer or integer valued vector indicating the size of the window for the polinomial fit. min(m) must be greater or equal than nu or else it will return an error.

nu

a non-negative integer denoting the degree of the polinomial fit applied on the integrated series.

G

the autocovariance matrix for the original time series. The dimension of G must be (max(m)+1) by (max(m)+1).

K

optional: the matrix K. If this matrix is provided and m is an integer, then nu is ignored.

Value

A vector of size length(m) containing the expected values of the detrended variance corresponding to the values of m provided. This is expression (20) in Prass and Pumi (2019).

Author(s)

Taiane Schaedler Prass

References

Prass, T.S. and Pumi, G. (2019). On the behavior of the DFA and DCCA in trend-stationary processes <arXiv:1910.10589>.

Examples

m = 3
K = Km(m = m, nu = 0)
G = diag(m+1)
EF2dfa(G = G, K = K)
# same as
EF2dfa(m = 3, nu = 0, G = G)

# An AR(1) example
phi = 0.4
n = 500
burn.in = 50
eps = rnorm(n + burn.in)
z.temp = numeric(n + burn.in)
z.temp[1] = eps[1]
for(i in 2:(n + burn.in)){
  z.temp[i] = phi*z.temp[i-1] + eps[i]
}
z = z.temp[(burn.in + 1):(n + burn.in)]

F2.dfa = F2dfa(z, m = 3:100, nu = 0, overlap = TRUE)
plot(3:100, F2.dfa, type="o", xlab = "m")

Expected value of the detrended cross-covariance

Description

Calculates the expected value of the detrended cross-covariance given a cross-covariance matrix.

Usage

EFdcca(m = 3, nu = 0, G, K = NULL)

Arguments

m

an integer or integer valued vector indicating the size of the window for the polinomial fit. min(m) must be greater or equal than nu or else it will result in an error.

nu

a non-negative integer denoting the degree of the polinomial fit applied on the integrated series.

G

the cross-covariance matrix for the original time series. The dimension of G must be (max(m)+1) by (max(m)+1).

K

optional: the matrix K. If this matrix and m are provided, then nu is ignored.

Value

a size length(m) vector containing the expected values of the detrended cross-covariance corresponding to the values of m provided. This is expression (23) in Prass and Pumi (2019).

Author(s)

Taiane Schaedler Prass

References

Prass, T.S. and Pumi, G. (2019). On the behavior of the DFA and DCCA in trend-stationary processes <arXiv:1910.10589>.

Examples

m = 3
K = Km(m = m, nu = 0)
G = diag(m+1)
EFdcca(G = G, K = K)
# same as
EFdcca(m = 3, nu = 0, G = G)

Detrended Variance

Description

Calculates the detrended variance based on a given time series.

Usage

F2dfa(y, m = 3, nu = 0, overlap = TRUE)

Arguments

y

vector corresponding to the time series data.

m

an integer or integer valued vector indicating the size (or sizes) of the window for the polinomial fit. min(m) must be greater or equal than nu or else it will return an error.

nu

a non-negative integer denoting the degree of the polinomial fit applied on the integrated series.

overlap

logical: if true (the default), uses overlapping windows. Otherwise, non-overlapping boxes are applied.

Value

A vector of size length(m) containing the detrended variance considering windows of size m+1, for each m supplied.

Author(s)

Taiane Schaedler Prass

References

Prass, T.S. and Pumi, G. (2019). On the behavior of the DFA and DCCA in trend-stationary processes <arXiv:1910.10589>.

Examples

# Simple usage
y = rnorm(100)
F2.dfa = F2dfa(y, m = 3, nu = 0, overlap = TRUE)
F2.dfa

vF2.dfa = F2dfa(y, m = 3:5, nu = 0, overlap = TRUE)
vF2.dfa


###################################################
# AR(1) example showing how the DFA varies with phi

phi = (1:8)/10
n = 300
z = matrix(nrow = n, ncol = length(phi))
for(i in 1:length(phi)){
  z[,i] = arima.sim(model = list(ar = phi[i]), n)
}

ms = 3:50
F2.dfa = matrix(ncol = length(phi), nrow = length(ms))

for(j in 1:length(phi)){
  F2.dfa[,j] = F2dfa(z[,j], m = ms  , nu = 0, overlap = TRUE)
}

cr = rainbow(length(phi))
plot(ms, F2.dfa[,1], type = "o", xlab = "m", col = cr[1],
    ylim = c(0,max(F2.dfa)), ylab = "F2.dfa")
for(j in 2:length(phi)){
  points(ms, F2.dfa[,j], type = "o", col = cr[j])
}
legend("topleft", lty = 1, legend = phi, col = cr, bty = "n", title = expression(phi), pch=1)


##############################################################################
# An MA(2) example showcasing why overlapping windows are usually advantageous
n = 300
ms = 3:50
theta = c(0.4,0.5)

# Calculating the expected value of the DFA in this scenario
m_max = max(ms)
vtheta = c(c(1,theta, rep(0, m_max - length(theta))))
G = matrix(0, ncol = m_max+1, nrow = m_max+1)
for(t in 1:(m_max+1)){
  for(h in 0:(m_max+1-t)){
    G[t,t+h] = sum(vtheta[1:(length(vtheta)-h)]*vtheta[(1+h):length(vtheta)])
    G[t+h,t] = G[t,t+h]
  }
}

EF2.dfa = EF2dfa(m = ms, nu = 0, G = G)

z = arima.sim(model = list(ma = theta), n)

ms = 3:50
OF2.dfa = F2dfa(z, m = ms, nu = 0, overlap = TRUE)
NOF2.dfa = F2dfa(z, m = ms, nu = 0, overlap = FALSE)

plot(ms, OF2.dfa, type = "o", xlab = "m", col = "blue",
    ylim = c(0,max(OF2.dfa,NOF2.dfa,EF2.dfa)), ylab = "F2.dfa")
points(ms, NOF2.dfa, type = "o", col = "darkgreen")
points(ms, EF2.dfa, type = "o", col = "red")
legend("bottomright", legend = c("overlapping","non-overlapping","expected"),
            col = c("blue", "darkgreen","red"), lty= 1, bty = "n", pch=1)

Detrended Cross-covariance

Description

Calculates the detrended cross-covariance between two time series y1 and y2.

Usage

Fdcca(y1, y2, m = 3, nu = 0, overlap = TRUE)

Arguments

y1, y2

vectors corresponding to the time series data. If length(y1) and length(y2) differ, the longer time series is coerced to match the lenght of the shorter.

m

an integer or integer valued vector indicating the size (or sizes) of the window for the polinomial fit. min(m) must be greater or equal than nu or else it will return an error.

nu

a non-negative integer denoting the degree of the polinomial fit applied on the integrated series.

overlap

logical: if true (the default), uses overlapping windows. Otherwise, non-overlapping boxes are applied.

Value

A vector of size length(m) containing the detrended cross-covariance considering windows of size m+1, for each m supplied.

Author(s)

Taiane Schaedler Prass

References

Prass, T.S. and Pumi, G. (2019). On the behavior of the DFA and DCCA in trend-stationary processes <arXiv:1910.10589>.

Examples

# Simple usage
y1 = rnorm(100)
y2 = rnorm(100)
F.dcca = Fdcca(y1, y2, m = 3, nu = 0, overlap = TRUE)
F.dcca

# A simple example where y1 and y2 are independent.

ms = 3:50
F.dcca1 = Fdcca(y1, y2, m = ms, nu = 0, overlap = TRUE)
F.dcca2 = Fdcca(y1, y2, m = ms, nu = 0, overlap = FALSE)

plot(ms, F.dcca1, type = "o", xlab = "m", col = "blue",
     ylim = c(min(F.dcca1,F.dcca2),max(F.dcca1,F.dcca2)),
     ylab = expression(F[DCCA]))
points(ms, F.dcca2, type = "o", col = "red")
legend("bottomright", legend = c("overlapping","non-overlapping"),
       col = c("blue", "red"), lty= 1, bty = "n", pch=1)


# A more elaborated example where y1 and y2 display cross-correlation for non-null lags.
# This example also showcases why overlapping windows are usually advantageous.
# The data generating process is the following:
# y1 is i.i.d. Gaussian while y2 is an MA(2) generated from y1.

n = 500
ms = 3:50
theta = c(0.4,0.5)

# Calculating the expected value of the DCCA in this scenario
m_max = max(ms)
vtheta = c(1,theta, rep(0, m_max - length(theta)))
G12 = matrix(0, ncol = m_max+1, nrow = m_max+1)
for(t in 1:(m_max+1)){
  for(h in 0:(m_max+1-t)){
    G12[t,t+h] = vtheta[h+1]
  }
}

EF.dcca = EFdcca(m = ms, nu = 0, G = G12)

# generating the series and calculating the DCCA
burn.in = 100
eps = rnorm(burn.in)

y1 = rnorm(n)
y2 = arima.sim(model = list(ma = theta), n, n.start = burn.in, innov = y1, start.innov = eps)

ms = 3:50
OF.dcca = Fdcca(y1, y2, m = ms, nu = 0, overlap = TRUE)
NOF.dcca = Fdcca(y1, y2, m = ms, nu = 0, overlap = FALSE)

plot(ms, OF.dcca, type = "o", xlab = "m", col = "blue",
     ylim = c(min(NOF.dcca,OF.dcca,EF.dcca),max(NOF.dcca,OF.dcca,EF.dcca)),
     ylab = expression(F[DCCA]))
points(ms, NOF.dcca, type = "o", col = "darkgreen")
points(ms, EF.dcca, type = "o", col = "red")
legend("bottomright", legend = c("overlapping","non-overlapping","expected"),
       col = c("blue", "darkgreen","red"), lty= 1, bty = "n", pch=1)

Matrix J

Description

Creates a n by n lower triangular matrix with all non-zero entries equal to one.

Usage

Jn(n = 2)

Arguments

n

number of rows and columns in the J matrix.

Value

an n by n lower triangular matrix with all non-zero entries equal to one. This is an auxiliary function.

Examples

J = Jn(n = 3)
J

The product of Kronecker Product of some Arrays

Description

This is an auxiliary function and requires some context to be used adequadely. It computes equation (19) in Prass and Pumi (2019), returning a square matrix defined by

K* = (Jm \%x\% J*)'(Q \%x\% Q)(Jm \%x\% J*)

where:

Usage

Kkronm(m = 3, nu = 0, h = 0, overlap = TRUE, K = NULL)

Arguments

m

a positive integer indicating the size of the window for the polinomial fit.

nu

a non-negative integer denoting the degree of the polinomial fit applied on the integrated series.

h

an integer indicating the lag.

overlap

logical: if true (the default), overlapping boxes are used for calculations. Otherwise, non-overlapping boxes are applied.

K

optional: the matrix defined by K = J'QJ. This is used to calculate K* = (Jm \%x\% J*)'(Q \%x\% Q)(Jm \%x\% J*). For details see (19) in Prass and Pumi (2019). If this matrix is provided mu is ignored.

Value

an (m+1)[(m+1)*(h+1) - m*h*s] by (m+1)[(m+1)*(h+1) - m*h*s] matrix, where s = 1 if overlap = TRUE and s = 0, otherwise. This matrix corresponds to equation (19) in Prass and Pumi (2019).

Author(s)

Taiane Schaedler Prass

References

Prass, T.S. and Pumi, G. (2019). On the behavior of the DFA and DCCA in trend-stationary processes <arXiv:1910.10589>.

See Also

Jn which creates the matrix J, Qm which creates Q and Km which creates K.

Examples

m = 3
h = 1
J = Jn(n = m+1+h)
Q = Qm(m = m, nu = 0)

# using K
K = Km(J = J[1:(m+1),1:(m+1)], Q = Q)
Kkron0 = Kkronm(K = K, h = h)

# using m and nu
Kkron = Kkronm(m = m, nu = 0, h = h)

# using  kronecker product from R
K = Km(J = J[1:(m+1),1:(m+1)], Q = Q)
Kh = rbind(matrix(0, nrow = h, ncol = m+1+h),
           cbind(matrix(0, nrow = m+1, ncol = h), K))
KkronR = K %x% Kh

# using  the definition K* = (Jm %x%  J)'(Q %x%  Q)(Jm %x%  J)
J_m = J[1:(m+1),1:(m+1)]
J_h = J[(h+1):(m+1+h),1:(m+1+h)]
KkronD = t(J_m %x%  J_h)%*%(Q %x%  Q)%*%(J_m %x%  J_h)


# comparing the results
sum(abs(Kkron0 - Kkron))
sum(abs(Kkron0 - KkronR))
sum(abs(Kkron0 - KkronD))  # difference due to rounding error

## Not run: 
# Function Kkronm is computationaly faster than a pure implementation in R:

m = 100
h = 1
J = Jn(n = m+1)
Q = Qm(m = m, nu = 0)

# using Kkronm
t1 = proc.time()
Kkron = Kkronm(m = m, nu = 0, h = 1)
t2 = proc.time()
# elapsed time:
t2-t1

# Pure R implementation:
K = Km(J = J, Q = Q)
Kh = rbind(matrix(0, nrow = h, ncol = m+1+h),
           cbind(matrix(0, nrow = m+1, ncol = h), K))
t3 = proc.time()
KkronR = K %x% Kh
t4 = proc.time()
# elapsed time
t4-t3


## End(Not run)

Matrix K

Description

This is an auxiliary function which computes expression (18) in Prass and Pumi (2019). It creates an m+1 by m+1 matrix defined by K = J'QJ where J is a m+1 by m+1 lower triangular matrix with all non-zero entries equal to one and Q is a m+1 by m+1 given by Q = I - P where P is the projection matrix into the subspace generated by degree nu+1 polynomials and I is the m+1 by m+1 identity matrix.

Usage

Km(m = 3, nu = 0, J = NULL, Q = NULL)

Arguments

m

a positive integer greater or equal than nu indicating the size of the window for the polinomial fit.

nu

a non-negative integer denoting the degree of the polinomial fit applied on the integrated series.

J, Q

optional: the matrices such that K = J'QJ. If both matrices are provided, m and nu are ignored.

Value

an m+1 by m+1 matrix corresponding to expression (18) in Prass and Pumi (2019).

Author(s)

Taiane Schaedler Prass

References

Prass, T.S. and Pumi, G. (2019). On the behavior of the DFA and DCCA in trend-stationary processes <arXiv:1910.10589>.

See Also

Jn which creates the matrix J, Qm which creates Q and Pm which creates P.

Examples

K = Km(m = 3, nu = 0)
K
# same as
m = 3
J = Jn(n = m+1)
Q = Qm(m = m, nu = 0)
K = Km(J = J, Q = Q)
K

Projection Matrix P

Description

Creates the m+1 by m+1 projection matrix defined by P = D(D'D)^{-1}D' where D is the design matrix associated to a polynomial regression of degree nu + 1.

Usage

Pm(m = 2, nu = 0)

Arguments

nu

the degree of the polinomial fit.

m

a positive integer satisfying m >= nu indicating the size of the window for the polinomial fit.

Details

To perform matrix inversion, the code makes use of the routine DGETRI in LAPACK, which applies an LU decomposition approach to obtain the inverse matrix. See the LAPACK documentation available at http://www.netlib.org/lapack.

Value

an m+1 by m+1 matrix.

Author(s)

Taiane Schaedler Prass

Examples

P = Pm(m = 5, nu = 0)
P

n = 10
t = 1:n
D = cbind(rep(1,n),t,t^2)

# Calculating in R
PR = D%*%solve(t(D)%*%D)%*%t(D)
# Using the provided function
P = Pm(m = n-1, nu = 1)

# Difference:
sum(abs(P-PR))

Projection Matrix Q

Description

Creates the m+1 by m+1 projection matrix defined by Q = I-P where I is the the m+1 by m+1 identity matrix and P is the m+1 by m+1 projection matrix into the space generated by polynomials of degree nu + 1.

Usage

Qm(m = 2, nu = 0, P = NULL)

Arguments

nu

the degree of the polinomial fit.

m

a positive integer satisfying m >= nu indicating the size of the window for the polinomial fit.

P

optional: the projection matrix such that Q = I - P (see function Pm). If this matrix is provided m and nu are ignored.

Value

an m+1 by m+1 matrix.

See Also

Pm which generates the projection matrix P.

Examples

Q = Qm(m = 3, nu = 0)
Q
# same as
P = Pm(m = 3, nu = 0)
Q = Qm(P = P)
Q

Autocovariance function of the detrended variance

Description

Calculates the autocovariance of the detrended variance.

Usage

covF2dfa(m = 3, nu = 0, h = 0, overlap = TRUE, G, Cumulants = NULL)

Arguments

m

an integer or integer valued vector indicating the size of the window for the polinomial fit. min(m) must be greater or equal than nu or else it will return an error.

nu

a non-negative integer denoting the degree of the polinomial fit applied on the integrated series.

h

an integer or integer valued vector indicating the lags for which the autocovariance function is to be calculated.

overlap

logical: if true (the default), overlapping boxes are used for calculations. Otherwise, non-overlapping boxes are applied.

G

the autocovariance matrix for the original time series. The dimension of G must be (max(m)+max(h)+1) by (max(m)+max(h)+1) if overlap = TRUE and (max(m)+max(h))(max(h)+1) by (max(m)+max(h))(max(h)+1) otherwise.

Cumulants

The matrix containing the joint cumulants for lags. Dimension must be (max(m)+1)*nrow(G). If not provided, it is assumed that the cumulants are all zero.

Value

A matrix with the autocovariance of lag h, for each value of m provided. This matrix is obtained from expressions (21) for h = 0 and (22) for h > 0 in Prass and Pumi (2019).

Author(s)

Taiane Schaedler Prass

References

Prass, T.S. and Pumi, G. (2019). On the behavior of the DFA and DCCA in trend-stationary processes <arXiv:1910.10589>.

Examples

## Not run: 
ms = seq(3,100,1)
hs = seq(0,50,1)
overlap = TRUE
nu = 0
m_max = (max(ms)+1)*(max(hs)+1) - max(ms)*max(hs)*as.integer(overlap)

theta = c(c(1,(20:1)/10), rep(0, m_max - 20))
Gamma1 = diag(m_max+1)
Gamma2 = matrix(0, ncol = m_max+1, nrow = m_max+1)
Gamma12 = matrix(0, ncol = m_max+1, nrow = m_max+1)
for(t in 1:(m_max+1)){
    for(h in 0:(m_max+1-t)){
        Gamma2[t,t+h] = sum(theta[1:(length(theta)-h)]*theta[(1+h):length(theta)])
        Gamma2[t+h,t] = Gamma2[t,t+h]
        Gamma12[t,t+h] = theta[h+1]
    }
}

covdfa1 = covF2dfa(m = ms, nu = 0, h = hs,
                   overlap = TRUE, G = Gamma1, Cumulants = NULL)

covdfa2 = covF2dfa(m = ms, nu = 0, h = hs,
                  overlap = TRUE, G = Gamma2, Cumulants = NULL)

cr = rainbow(100)
plot(ms, covdfa1[,1], type = "l", ylim = c(0,20),
    xlab = "m", ylab = expression(gamma[DFA](h)), col = cr[1])
for(i in 2:ncol(covdfa1)){
  points(ms, covdfa1[,i],  type = "l", col = cr[i])
}

lattice::wireframe(covdfa1, drape = TRUE,
    col.regions = rev(rainbow(150))[50:150],
    zlab = expression(gamma[DFA]), xlab = "m", ylab = "h")

## End(Not run)

Autocovariance function of the detrended cross-covariance

Description

Calculates the autocovariance of the detrended cross-covariance.

Usage

covFdcca(m = 3, nu = 0, h = 0, overlap = TRUE, G1, G2, G12, Cumulants = NULL)

Arguments

m

an integer or integer valued vector indicating the size of the window for the polinomial fit. min(m) must be greater or equal than nu or else it will return an error.

nu

a non-negative integer denoting the degree of the polinomial fit applied on the integrated series.

h

an integer or integer valued vector indicating the lags for which the autocovariance function is to be calculated. Negative values are not allowed.

overlap

logical: if true (the default), overlapping boxes are used for calculations. Otherwise, non-overlapping boxes are applied.

G1, G2

the autocovariance matrices for the original time series. The dimension of G1 and G2 must be compatible with the highest values in vectors m and h. More specifically, the dimension of G1 and G2 is (max(m)+max(h)+1) by (max(m)+max(h)+1) if overlap = TRUE and dim(G1) = dim(G2) = (max(m)+max(h))(max(h)+1) by (max(m)+max(h))(max(h)+1) otherwise.

G12

the cross-covariance matrix for the original time series. The dimension of G12 must be compatible with the highest values in vectors m and h. If overlap = TRUE, dim(G12) = [(max(m)+1)*(max(h)+1) - max(m)*max(h)] by [(max(m)+1)*(max(h)+1) - max(m)*max(h)] and dim(G12) = [(max(m)+1)*(max(h)+1)] by [max(m)+1)*(max(h)+1)], otherwise

Cumulants

The matrix of cumulants. If not provided, it is assumed that the cumulants are all zero.

Value

A matrix of dimension lenght(h) by length(m) with the autocovariance of lag h (rows), for each value of m (columns) provided. This matrix is obtained from expressions (24) for h = 0 and (25) for h > 0 in Prass and Pumi (2019).

Author(s)

Taiane Schaedler Prass

References

Prass, T.S. and Pumi, G. (2019). On the behavior of the DFA and DCCA in trend-stationary processes <arXiv:1910.10589>.

Examples

## Not run: 
ms = seq(3,100,1)
hs = seq(0,50,1)
overlap = TRUE
nu = 0
m_max = (max(ms)+1)*(max(hs)+1) - max(ms)*max(hs)*as.integer(overlap)

theta = c(c(1,(20:1)/10), rep(0, m_max - 20))
Gamma1 = diag(m_max+1)
Gamma2 = matrix(0, ncol = m_max+1, nrow = m_max+1)
Gamma12 = matrix(0, ncol = m_max+1, nrow = m_max+1)
for(t in 1:(m_max+1)){
    for(h in 0:(m_max+1-t)){
        Gamma2[t,t+h] = sum(theta[1:(length(theta)-h)]*theta[(1+h):length(theta)])
        Gamma2[t+h,t] = Gamma2[t,t+h]
        Gamma12[t,t+h] = theta[h+1]
    }
}

covdcca = covFdcca(m = ms, nu = 0, h = hs,
                   G1 = Gamma1, G2 = Gamma2, G12 = Gamma12)
                   
## End(Not run)

The limit value of the detrended cross-covariance

Description

Calculates the theoretical counterpart of the cross-correlation coefficient. This is expression (11) in Prass and Pumi (2019). For trend-stationary processes under mild assumptions, this is equivalent to the limit of the detrended cross correlation coefficient calculated with window of size m+1 as m tends to infinity (see theorem 3.2 in Prass and Pumi, 2019).

Usage

rhoE(m = 3, nu = 0, G1, G2, G12, K = NULL)

Arguments

m

an integer or integer valued vector indicating the size (or sizes) of the window for the polinomial fit. min(m) must be greater or equal than nu or else it will return an error.

nu

a non-negative integer denoting the degree of the polinomial fit applied on the integrated series.

G1, G2

the autocovariance matrices for the original time series. Both are max(m)+1 by max(m)+1 matrices.

G12

the cross-covariance matrix for the original time series. The dimension of G12 must be max(m)+1) by max(m)+1).

K

optional: the matrix K. See the details.

Details

The optional argument K is an m+1 by m+1 matrix defined by K = J'QJ, where J is a m+1 by m+1 lower triangular matrix with all non-zero entries equal to one and Q is a m+1 by m+1 given by Q = I - P where P is the projection matrix into the subspace generated by degree nu+1 polynomials and I is the m+1 by m+1 identity matrix. K is equivalent to expression (18) in Prass and Pumi (2019). If this matrix is provided and m is an integer, then nu are ignored.

Value

A list containing the following elements, calculated considering windows of size m+1, for each m supplied:

EF2dfa1, EF2dfa2

the expected values of the detrended variances.

EFdcca

the expected value of the detrended cross-covariance.

rhoE

the vector with the theoretical counterpart of the cross-correlation coefficient.

Author(s)

Taiane Schaedler Prass

References

Prass, T.S. and Pumi, G. (2019). On the behavior of the DFA and DCCA in trend-stationary processes <arXiv:1910.10589>.

See Also

Km which creates the matrix K, Jn which creates the matrix J, Qm which creates Q and Pm which creates P.

Examples

m = 3
K = Km(m = m, nu = 0)
G1 = G2 =  diag(m+1)
G12 = matrix(0,ncol = m+1, nrow = m+1)
rhoE(G1 = G1, G2 = G2, G12 = G12, K = K)
# same as
rhoE(m = 3, nu = 0, G1 = G1, G2 = G2, G12 = G12)

Detrended Cross-correlation coefficient

Description

Calculates the detrended cross-correlation coefficient for two time series y1 and y2.

Usage

rhodcca(y1, y2, m = 3, nu = 0, overlap = TRUE)

Arguments

y1, y2

vectors corresponding to the time series data. If length(y1) and length(y2) differ, the longer time series is coerced to match the lenght of the shorter.

m

an integer value or a vector of integer values indicating the size of the window for the polinomial fit. min(m) must be greater or equal than nu or else it will return an error.

nu

the degree of the polynomial fit

overlap

logical: if true (the default), uses overlapping windows. Otherwise, non-overlapping boxes are applied.

Value

A list containing the following elements, calculated considering windows of size m+1, for each m supplied:

F2dfa1, F2dfa2

The detrended variances for y1 and y2, respectively.

Fdcca

The detrended cross-covariance.

rhodcca

The detrended cross-correlation coefficient.

Note

The time series y1 and y2 must have the same sample size.

Author(s)

Taiane Schaedler Prass

References

Prass, T.S. and Pumi, G. (2019). On the behavior of the DFA and DCCA in trend-stationary processes <arXiv:1910.10589>.

See Also

F2dfa which calculated the DFA and Fdcca which calculated the DCCA of two given time series.

Examples

y1 = rnorm(100)
y2 = rnorm(100)
rho.dccam1 = rhodcca(y1, y2, m = 3, nu = 0, overlap = TRUE)
rho.dccam1

rho.dccam2 = rhodcca(y1, y2, m = c(3,6,8), nu = 0, overlap = TRUE)
rho.dccam2