inst/doc/the_bridgedist_basics.R

In bridgedist: An Implementation of the Bridge Distribution with Logit-Link as in Wang and Louis (2003)

## ---- eval=TRUE---------------------------------------------------------------
library(bridgedist)

## ---- eval=FALSE--------------------------------------------------------------
#  xaxis <- seq(-3,3,.01)
#  plot(xaxis, dbridge(xaxis, phi=1/sqrt(1+3/pi^2)), type="l",
#       xlab="x", ylab="density(x)")
#  lines(xaxis, dnorm(xaxis))
#  lines(xaxis, dlogis(xaxis, phi=sqrt(3/pi^2)))

## ---- fig.width=6, fig.cap = "Fig. 1. Probability density functions of the Gaussian, logistic and bridge, for logistic, distributions each with zero mean and unit variance."----
library(reshape2)
library(ggplot2)
xaxis = seq(-4,4,.01)
df = data.frame( xaxis,
                 Bridge = dbridge(xaxis, phi=1/sqrt(1+3/pi^2)),
                 Normal = dnorm(xaxis),
                 Logistic = dlogis(xaxis, scale=sqrt(3/pi^2)))
melt.df <- melt(df, id.vars = "xaxis")
colnames(melt.df) <- c("x", "Distribution", "value")
ggplot(melt.df, aes(x, value, color=Distribution)) + 
  geom_line(size=1.05) + 
  ylab("Probability density function") 

## ---- fig.width=6, fig.cap = "Fig. 2. 10000 random variates in each panel.  From left to right: the bridge distribution, the logistic with scale=1, the sum of the previous two, and the logistic with scale=1/phi.  Note how similar the third and fourth panel, the application supporting the theory.", warning=FALSE, message=FALSE----
phi <- 0.5
df = data.frame(
                 Bridge = rbridge(1e5, phi=phi),
                 Std_Logistic = rlogis(1e5),
                 BridgePlusStd_Logistic = rbridge(1e5, phi=phi) +  rlogis(1e5),
                 Logistic = rlogis(1e5, scale=1/phi)
)
melt.df <- melt(df)
colnames(melt.df) <- c("Distribution", "value")
ggplot(melt.df, aes(value)) +
  facet_grid(.~Distribution) +
  geom_histogram()