/
gamma.R
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gamma.R
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# Draw the gamma distribution.
library(ggplot2)
x <- seq(0, 100, 0.001)
#a <- 0.5
a <- 1.5
s <- 2
i<- seq(0,100,0.001)
y=dgamma(i, shape = a, scale = s)
y[length(y)] <-0
# graphics margins:
margins<-c(4.5,4.5,1,2)
# C<- data.frame(x,y)
B <- matrix(c(i,y), nrow=length(i),ncol=2)
C <-data.frame(B)
png(filename="gammadistribution.png",
width=5,
height=5,
units="in",
pointsize=10,
bg="white",
res=300,
type="quartz")
plot(x,
dgamma(x, shape = a, scale = s),
type = "l",
ylim = c(0,0.3),
lwd = 2,
xlab="X value",
ylab="Probability of event occurrence",
xlim=c(0,10)
)
# polygon(c(i),dgamma(i, shape = a, scale = s), density=5, angle=45)
polygon(c(i),dgamma(i, shape = a, scale = s), col="darkgreen")
text(6, 1.4, expression(f(x) == frac(1, s^a * Gamma(a)) * x^(a - 1) * exp(-frac(x, s))))
text(6, 1.2, expression(paste(a > 0, ": shape parameter")))
text(6, 1.1, expression(paste(s > 0, ": scale parameter")))
title("Gamma distribution: parameters shape=1.5 and scale=2",cex = 0.6)
dev.off()
png(filename="gammadistribution_simple.png",
width=5,
height=5,
units="in",
pointsize=10,
bg="white",
res=300,
type="quartz")
par(mar=margins)
plot(x, dgamma(x, shape = a, scale = s), type = "l",
ylim = c(0,0.3),
xlim=c(0,10),
lwd = 2,
xlab="X value",
ylab="Probability of event occurrence")
# polygon(c(i),dgamma(i, shape = a, scale = s), density=5, angle=45)
polygon(c(i),dgamma(i, shape = a, scale = s), col="darkgreen")
#text(6, 1.4, expression(f(x) == frac(1, s^a * Gamma(a)) * x^(a - 1) * exp(-frac(x, s))))
#text(6, 1.2, expression(paste(a > 0, ": shape parameter")))
#text(6, 1.1, expression(paste(s > 0, ": scale parameter")))
#title("Gamma distribution: parameters shape=1.5 and scale=2",cex = 0.6)
dev.off()
png(filename="gammadistributionnolabels.png", width=5, height=5, units="in", pointsize=10, bg="white", res=300, type="quartz")
bb <- ggplot(data=C, aes(x=i,y=y)) +
geom_point(size=0.5, color="darkgreen") +
labs( x="X value", y="Probability") +
geom_polygon(x=i,y=y, fill="darkgreen", size=0.5, alpha=1) +
xlim(0,10)
bb
dev.off()