| CIRCcop {copBasic} | R Documentation |
Copula of Circular Uniform Distribution
Description
The Circular copula of the coordinates (x, y) of a point chosen at random on the unit circle (Nelsen, 2006, p. 56) is given by
\mathbf{C}_{\mathrm{CIRC}}(u,v) = \mathbf{M}(u,v) \mathrm{\ for\ }|u-v| > 1/2\mathrm{,}
\mathbf{C}_{\mathrm{CIRC}}(u,v) = \mathbf{W}(u,v) \mathrm{\ for\ }|u+v-1| > 1/2\mathrm{,\ and}
\mathbf{C}_{\mathrm{CIRC}}(u,v) = \frac{u+v}{2} - \frac{1}{4} \mathrm{\ otherwise\ }\mathrm{.}
The coordinates of the unit circle are given by
\mathrm{CIRC}(x,y) = \biggl(\frac{\mathrm{cos}\bigl(\pi(u-1)\bigr)+1}{2}, \frac{\mathrm{cos}\bigl(\pi(v-1)\bigr)+1}{2}\biggr)\mathrm{.}
Usage
CIRCcop(u, v, para=NULL, as.circ=FALSE, ...)
Arguments
u |
Nonexceedance probability |
v |
Nonexceedance probability |
para |
Optional parameter list argument that can contain the logical |
as.circ |
A logical, if true, to trigger the transformation |
... |
Additional arguments to pass, if ever needed. |
Value
Value(s) for the copula are returned.
Author(s)
W.H. Asquith
References
Nelsen, R.B., 2006, An introduction to copulas: New York, Springer, 269 p.
Examples
CIRCcop(0.5, 0.5) # 0.25 quarterway along the diagonal upward to right
CIRCcop(0.5, 1 ) # 0.50 halfway across in horizontal direction
CIRCcop(1 , 0.5) # 0.50 halfway across in vertical direction
## Not run:
nsim <- 2000
rtheta <- runif(nsim, min=0, max=2*pi) # polar coordinate simulation
XY <- data.frame(X=cos(rtheta)/2 + 1/2, Y=sin(rtheta)/2 + 1/2)
plot(XY, lwd=0.8, col="lightgreen", xaxs="i", yaxs="i", las=1,
xlab="X OF UNIT CIRCLE OR NONEXCEEDANCE PROBABILITY U",
ylab="Y OF UNIT CIRCLE OR NONEXCEEDANCE PROBABILITY V")
UV <- simCOP(nsim, cop=CIRCcop, lwd=0.8, col="salmon3", ploton=FALSE)
theta <- 3/4*pi+0.1 # select a point on the upper left of the circle
x <- cos(theta)/2 + 1/2; y <- sin(theta)/2 + 1/2 # coordinates
H <- CIRCcop(x, y, as.circ=TRUE) # 0.218169 # Pr[X <= x & Y <= y]
points(x, y, pch=16, col="forestgreen", cex=2)
segments(0, y, x, y, lty=2, lwd=2, col="forestgreen")
segments(x, 0, x, y, lty=2, lwd=2, col="forestgreen")
Hemp1 <- sum(XY$X <= x & XY$Y <= y) / nrow(XY) # about 0.22 as expected
u <- 1-acos(2*x-1)/pi; v <- 1-acos(2*y-1)/pi
segments(0, v, u, v, lty=2, lwd=2, col="salmon3")
segments(u, 0, u, v, lty=2, lwd=2, col="salmon3")
points(u, v, pch=16, cex=2, col="salmon3")
arrows(x, y, u, v, code=2, lwd=2, angle=15) # arrow points from (X,Y) coordinate
# specified by angle theta in radians on the unit circle to the corresponding
# coordinate in (U,V) domain of uniform circular distribution copula
Hemp2 <- sum(UV$U <= u & UV$V <= v) / nrow(UV) # about 0.22 as expected
# Hemp1 and Hemp2 are about equal to each other and converge as nsim
# gets very large, but the origin of the simulations to get to each
# are different: (1) one in polar coordinates and (2) by copula.
# Now, draw the level curve for the empirical Hs and as nsim gets large the two
# lines will increasingly plot on top of each other.
lshemp1 <- level.setCOP(cop=CIRCcop, getlevel=Hemp1, lines=TRUE, col="blue", lwd=2)
lshemp2 <- level.setCOP(cop=CIRCcop, getlevel=Hemp2, lines=TRUE, col="blue", lwd=2)
txt <- paste0("level curves for Pr[X <= x & Y <= y] and\n",
"level curves for Pr[U <= u & V <= v],\n",
"which equal each other as nsim gets large")
text(0.52, 0.52, txt, srt=-46, col="blue") #
## End(Not run)
## Not run:
# Nelsen (2007, ex. 3.2, p. 57) # Singular bivariate distribution with
# standard normal margins that is not bivariate normal.
U <- runif(500); V <- simCOPmicro(U, cop=CIRCcop)
X <- qnorm(U, mean=0, sd=1); Y <- qnorm(V, mean=0, sd=1)
plot(X,Y, main="Nelsen (2007, ex. 3.2, p. 57)", xlim=c(-4,4), ylim=c(-4,4),
lwd=0.8, col="turquoise")
rug(X, side=1, col=grey(0,0.5), tcl=0.5)
rug(Y, side=2, col=grey(0,0.5), tcl=0.5) #
## End(Not run)
## Not run:
DX <- c(5, 5, -5, -5); DY <- c(5, 5, -5, -5); D <- 6; R <- D/2
plot(DX, DY, type="n", xlim=c(-10, 10), ylim=c(-10,10), xlab="X", ylab="Y")
abline(h=DX, lwd=2, col="seagreen"); abline(v=DY, lwd=2, col="seagreen")
for(i in seq_len(length(DX))) {
for(j in seq_len(length(DY))) {
UV <- simCOP(n=30, cop=CIRCcop, pch=16, col="darkgreen", cex=0.5, graphics=FALSE)
points(UV[,1]-0.5, UV[,2]-0.5, pch=16, col="darkgreen", cex=0.5)
XY <- data.frame(X=DX[i]+sign(DX[i])*D*(cos(pi*(UV$U-1))+1)/2-sign(DX[i])*R,
Y=DY[j]+sign(DY[j])*D*(cos(pi*(UV$V-1))+1)/2-sign(DY[j])*R)
points(XY, lwd=0.8, col="darkgreen")
}
abline(h=DX[i]+R, lty=2, col="seagreen"); abline(h=DX[i]-R, lty=2, col="seagreen")
abline(v=DY[i]+R, lty=2, col="seagreen"); abline(v=DY[i]-R, lty=2, col="seagreen")
} #
## End(Not run)
## Not run:
para <- list(cop1=CIRCcop, para1=NULL, cop2=W, para2=NULL, alpha=0.8, beta=0.8)
UV <- simCOP(n=2000, col="darkgreen", cop=composite2COP, para=para)
XY <- data.frame(X=(cos(pi*(UV$U-1))+1)/2, Y=(cos(pi*(UV$V-1))+1)/2)
plot(XY, type="n", xlab=paste0("X OF CIRCULAR UNIFORM DISTRIBUTION OR\n",
"NONEXCEEDANCD PROBABILITY OF U"),
ylab=paste0("Y OF CIRCULAR UNIFORM DISTRIBUTION OR\n",
"NONEXCEEDANCD PROBABILITY OF V"))
JK <- data.frame(U=1 - acos(2*XY$X - 1)/pi, V=1 - acos(2*XY$Y - 1)/pi)
segments(x0=UV$U, y0=UV$V, x1=XY$X, y1=XY$Y, col="lightgreen", lwd=0.8)
points(XY, lwd=0.8, col="darkgreen")
points(JK, pch=16, col="darkgreen", cex=0.5)
t <- seq(0.001, 0.999, by=0.001)
t <- diagCOPatf(t, cop=composite2COP, para=para)
AB <- data.frame(X=(cos(pi*(t-1))+1)/2, Y=(cos(pi*(t-1))+1)/2)
lines(AB, lwd=4, col="seagreen") #
## End(Not run)