generateRFFast {CoSMoS}

Faster simulation of random fields with approximately separable spatiotemporal correlation structure

Description

For more details see section 6 in Serinaldi and Kilsby (2018), and section 2.4 in Papalexiou and Serinaldi (2020).

Usage

generateRFFast(
  n,
  spacepoints,
  margdist,
  margarg,
  p0,
  distbounds = c(-Inf, Inf),
  stcsid,
  stcsarg,
  scalefactor = 1,
  anisotropyid = "affine",
  anisotropyarg = list(phi1 = 1, phi2 = 1, phi12 = 0, theta = 0)
)

Arguments

n

number of fields (time steps) to simulate

spacepoints

side length m of the square field (m x m)

margdist

target marginal distribution of the field

margarg

list of marginal distribution arguments. Please consult the documentation of the selected marginal distribution indicated in the argument margdist for the list of required parameters

p0

probability zero

distbounds

distribution bounds (default set to c(-Inf, Inf))

stcsid

spatiotemporal correlation structure ID

stcsarg

list of spatiotemporal correlation structure arguments. Please consult the documentation of the selected spatiotemporal correlation structure indicated in the argument stcsid for the list of required parameters

scalefactor

factor specifying the distance between the centers of two pixels (default set to 1)

anisotropyid

spatial anisotropy ID (affine by default, swirl or wave)

anisotropyarg

list of arguments characterizing the spatial anisotropy according to the syntax of the function anisotropyT. Isotropic fields by default

Details

generateRFFast provides a faster approach to RF simulation compared to generateRF by exploiting circulant embedding fast Fourier transformation. However, this approach is feasible only for approximately separable target spatiotemporal correlation functions. generateRFFast comprises fitting and simulation in a single function. Here, we give indicative CPU times for some settings, referring to a Windows 10 Pro x64 laptop with Intel(R) Core(TM) i7-6700HQ CPU @ 2.60GHz, 4-core, 8 logical processors, and 32GB RAM.
CPU time:
m = 50, n = 1000: ~58s
m = 50, n = 10000: ~160s
m = 100, n = 1000: ~2955s (~50min)

References

Serinaldi, F., Kilsby, C.G. (2018). Unsurprising Surprises: The Frequency of Record-breaking and Overthreshold Hydrological Extremes Under Spatial and Temporal Dependence. Water Resources Research, 54(9), 6460-6487, doi: 10.1029/2018WR023055

Papalexiou, S.M., Serinaldi, F. (2020). Random Fields Simplified: Preserving Marginal Distributions, Correlations, and Intermittency, With Applications From Rainfall to Humidity. Water Resources Research, 56(2), e2019WR026331, doi: 10.1029/2019WR026331

Examples

sim <- generateRFFast(
    n = 50,
    spacepoints = 3,
    p0 = 0.7,
    margdist ='paretoII',
    margarg = list(scale = 1,
                   shape = .3),
    stcsarg = list(scfid = "weibull",
                   tcfid = "weibull",
                   scfarg = list(scale = 20,
                                 shape = 0.7),
                   tcfarg = list(scale = 1.1,
                                 shape = 0.8))
)

checkRF(sim,
          lags = 10,
          nfields = 49)