lognormgpd: Log-Normal Bulk and GPD Tail Extreme Value Mixture Model
In evmix: Extreme Value Mixture Modelling, Threshold Estimation and Boundary Corrected Kernel Density Estimation

Description Usage Arguments Details Value Note Author(s) References See Also Examples

Density, cumulative distribution function, quantile function and random number generation for the extreme value mixture model with log-normal for bulk distribution upto the threshold and conditional GPD above threshold. The parameters are the log-normal mean lnmean and standard deviation lnsd, threshold u GPD scale sigmau and shape xi and tail fraction phiu.

dlognormgpd(x, lnmean = 0, lnsd = 1, u = qlnorm(0.9, lnmean, lnsd),
  sigmau = lnsd, xi = 0, phiu = TRUE, log = FALSE)

plognormgpd(q, lnmean = 0, lnsd = 1, u = qlnorm(0.9, lnmean, lnsd),
  sigmau = lnsd, xi = 0, phiu = TRUE, lower.tail = TRUE)

qlognormgpd(p, lnmean = 0, lnsd = 1, u = qlnorm(0.9, lnmean, lnsd),
  sigmau = lnsd, xi = 0, phiu = TRUE, lower.tail = TRUE)

rlognormgpd(n = 1, lnmean = 0, lnsd = 1, u = qlnorm(0.9, lnmean,
  lnsd), sigmau = lnsd, xi = 0, phiu = TRUE)

`x`	quantiles
`lnmean`	mean on log scale
`lnsd`	standard deviation on log scale (positive)
`u`	threshold
`sigmau`	scale parameter (positive)
`xi`	shape parameter
`phiu`	probability of being above threshold [0, 1] or `TRUE`
`log`	logical, if TRUE then log density
`q`	quantiles
`lower.tail`	logical, if FALSE then upper tail probabilities
`p`	cumulative probabilities
`n`	sample size (positive integer)

Extreme value mixture model combining log-normal distribution for the bulk below the threshold and GPD for upper tail.

The user can pre-specify phiu permitting a parameterised value for the tail fraction φ_u. Alternatively, when phiu=TRUE the tail fraction is estimated as the tail fraction from the log-normal bulk model.

The cumulative distribution function with tail fraction φ_u defined by the upper tail fraction of the log-normal bulk model (phiu=TRUE), upto the threshold 0 < x ≤ u, given by:

F(x) = H(x)

and above the threshold x > u:

F(x) = H(u) + [1 - H(u)] G(x)

where H(x) and G(X) are the log-normal and conditional GPD cumulative distribution functions (i.e. plnorm(x, lnmean, lnsd) and pgpd(x, u, sigmau, xi)) respectively.

The cumulative distribution function for pre-specified φ_u, upto the threshold 0 < x ≤ u, is given by:

F(x) = (1 - φ_u) H(x)/H(u)

and above the threshold x > u:

F(x) = φ_u + [1 - φ_u] G(x)

Notice that these definitions are equivalent when φ_u = 1 - H(u).

The log-normal is defined on the positive reals, so the threshold must be positive.

See gpd for details of GPD upper tail component and dlnorm for details of log-normal bulk component.

dlognormgpd gives the density, plognormgpd gives the cumulative distribution function, qlognormgpd gives the quantile function and rlognormgpd gives a random sample.

All inputs are vectorised except log and lower.tail. The main inputs (x, p or q) and parameters must be either a scalar or a vector. If vectors are provided they must all be of the same length, and the function will be evaluated for each element of vector. In the case of rlognormgpd any input vector must be of length n.

Default values are provided for all inputs, except for the fundamentals x, q and p. The default sample size for rlognormgpd is 1.

Missing (NA) and Not-a-Number (NaN) values in x, p and q are passed through as is and infinite values are set to NA. None of these are not permitted for the parameters.

Error checking of the inputs (e.g. invalid probabilities) is carried out and will either stop or give warning message as appropriate.

Yang Hu and Carl Scarrott carl.scarrott@canterbury.ac.nz

http://en.wikipedia.org/wiki/Log-normal_distribution

http://en.wikipedia.org/wiki/Generalized_Pareto_distribution

Scarrott, C.J. and MacDonald, A. (2012). A review of extreme value threshold estimation and uncertainty quantification. REVSTAT - Statistical Journal 10(1), 33-59. Available from http://www.ine.pt/revstat/pdf/rs120102.pdf

Solari, S. and Losada, M.A. (2004). A unified statistical model for hydrological variables including the selection of threshold for the peak over threshold method. Water Resources Research. 48, W10541.

gpd and dlnorm

Other lognormgpd: flognormgpdcon, flognormgpd, lognormgpdcon

Other lognormgpdcon: flognormgpdcon, flognormgpd, lognormgpdcon

Other normgpd: fgng, fhpd, fitmnormgpd, flognormgpd, fnormgpdcon, fnormgpd, gngcon, gng, hpdcon, hpd, itmnormgpd, lognormgpdcon, normgpdcon, normgpd

Other flognormgpd: flognormgpd

## Not run: 
set.seed(1)
par(mfrow = c(2, 2))

x = rlognormgpd(1000)
xx = seq(-1, 10, 0.01)
hist(x, breaks = 100, freq = FALSE, xlim = c(-1, 10))
lines(xx, dlognormgpd(xx))

# three tail behaviours
plot(xx, plognormgpd(xx), type = "l")
lines(xx, plognormgpd(xx, xi = 0.3), col = "red")
lines(xx, plognormgpd(xx, xi = -0.3), col = "blue")
legend("bottomright", paste("xi =",c(0, 0.3, -0.3)),
  col=c("black", "red", "blue"), lty = 1)

x = rlognormgpd(1000, u = 2, phiu = 0.2)
hist(x, breaks = 100, freq = FALSE, xlim = c(-1, 10))
lines(xx, dlognormgpd(xx, u = 2, phiu = 0.2))

plot(xx, dlognormgpd(xx, u = 2, xi=0, phiu = 0.2), type = "l")
lines(xx, dlognormgpd(xx, u = 2, xi=-0.2, phiu = 0.2), col = "red")
lines(xx, dlognormgpd(xx, u = 2, xi=0.2, phiu = 0.2), col = "blue")
legend("topright", c("xi = 0", "xi = 0.2", "xi = -0.2"),
  col=c("black", "red", "blue"), lty = 1)

## End(Not run)