indicator_sdr: Spectral Density Ratio (SDR) indicator

Description Usage Arguments Details Value References See Also Examples

View source: R/indicator_sdr.R

Description

Compute the ratio of low frequencies over high frequencies of the r-spectrum. It also computes a null value obtained by randomizing the matrix.

Usage

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indicator_sdr(input, sdr_low_range = NULL, sdr_high_range = NULL,
  nreplicates = 999)

Arguments

input

A matrix or a logical matrix (TRUE/FALSE), or a list of these.

sdr_low_range

The range of values (in proportion) to use for the computation of the spectral density ratio. For example, for the lowest 20% (default value), set sdr_low_range to c(0, .2).

sdr_high_range

The range of values (in proportion) to use for the computation of the spectral density ratio. For example, for the highest 20% (default value), set sdr_high_range to c(.8, 1).

nreplicates

The number of replicates to compute for the null distribution

Details

SDR measures the increase in long-range correlations before a critical point. It is the ratio of the average low frequency value over high frequency values. In this implementation, an increase in SDR implies a "reddening" of the r-spectrum. See also spectral_spews for a more complete description.

Low and high frequencies are averaged in order to compute the SDR. The parameters sdr_low_range and sdr_high_range control which frequencies are selected for averaging. For example sdr_low_range = c(0, .2) (default) uses the lower 20 the average of low frequencies. sdr_high_range = c(.8, 1) uses the higher 20

Value

A list (or a list of lists if input was a list of matrices) with components:

If nreplicates is above 2, then the list has the following additional components :

References

Carpenter, S.R. & Brock, W.A. (2010). Early warnings of regime shifts in spatial dynamics using the discrete Fourier transform. Ecosphere

See Also

spectral_spews, rspectrum

Examples

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## Not run:  
serengeti.sdr <- indicator_sdr(serengeti, nreplicates = 499)
do.call(rbind, serengeti.sdr) # convert results to data.frame

## End(Not run)

spatialwarnings documentation built on Jan. 27, 2018, 3:01 a.m.