Variance Gamma Quantile-Quantile and Percent-Percent Plots
qqvg produces a variance gamma Q-Q plot of the values in
y.
ppvg produces a variance gamma P-P (percent-percent) or
probability plot of the values in y.
Graphical parameters may be given as arguments to qqvg and
ppvg.
qqvg(y, vgC = NULL, sigma = NULL, theta = NULL, nu = NULL,
param = c(vgC, sigma, theta, nu), main = "Variance Gamma Q-Q Plot",
xlab = "Theoretical Quantiles", ylab = "Sample Quantiles",
plot.it = TRUE, line = TRUE, ...)
ppvg(y, vgC = NULL, sigma = NULL, theta = NULL, nu = NULL,
param = c(vgC, sigma, theta, nu), main = "Variance Gamma P-P Plot",
xlab = "Uniform Quantiles",
ylab = "Probability-integral-transformed Data", plot.it = TRUE,
line = TRUE, ...)y |
The data sample. |
vgC |
The location parameter c, default is 0. |
sigma |
The spread parameter sigma, default is 1, must be positive. |
theta |
The asymmetry parameter theta, default is 0. |
nu |
The shape parameter nu, default is 1, must be positive. |
param |
An optional option, specifying the parameters as a vector
which takes the form |
main |
Plot title. |
xlab, ylab |
Plot labels. |
plot.it |
Logical. Should the result be plotted? |
line |
Add line through origin with unit slope. |
... |
Further graphical parameters. |
Users may specify the parameter values of the data sample y using
argument param. If param is not specified by users, then
the values are estimated from y by vgFit. For more details of
fiting a variance gamma distribution to data, see vgFit.
For qqvg and ppvg, a list with components:
x |
The x coordinates of the points that are to be plotted. |
y |
The y coordinates of the points that are to be plotted. |
David Scott d.scott@auckland.ac.nz, Christine Yang Dong c.dong@auckland.ac.nz
Wilk, M. B. and Gnanadesikan, R. (1968) Probability plotting methods for the analysis of data. Biometrika. 55, 1–17.
## Example 1: the parameter values are known par(mfrow = c(1,2)) y <- rvg(200, param = c(2,2,1,2)) qqvg(y, param = c(2,2,1,2),line = FALSE) abline(0, 1, col = 2) ppvg(y, param = c(2,2,1,2)) ## Example 2: the parameter values are unknown par(mfrow = c(1,2)) y <- rvg(200, param = c(2,2,1,2)) qqvg(y, line = FALSE) abline(0, 1, col = 2) ppvg(y)
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