stplanr (version 0.0.2)

dd_logcub: Cubic logarithmic decay function

Description

Function for converting distance of a trip into the probability of travel by a particular mode.

Usage

dd_logcub(x, a, b1, b2, b3)

Arguments

x

A positive vector representing distances (often in km)

a

Positive number (usually between 0 and 1) representing the intercept of the distance decay curve with the y axis, when x = 0.

b1

The linear term of distance decay

b2

The square term of distance decay

b3

The cubic term of distance decay - should be negative to converge to 0

Examples

x <- 0:10 # vector of distances
(res <- dd_logcub(x = x, a = 0.3, b1 = 0.003, b2 = -0.002, b3 = -0.001))
plot(x, res)

p1 <- c(0.05, -0.1489583, -0.002273, 0.0001945) # male distance decay
p2 <- c(0.10, -0.8396819, 0.0655261, -0.0017932) # female distance decay
x = seq(0, 20, 0.1)
ym <- dd_logcub(x, p1[1], p1[2], p1[3], p1[4])
yf <- dd_logcub(x, p2[1], p2[2], p2[3], p2[4])
plot(x, ym, ylim = c(0, 0.1)) # test plots
lines(x, yf) # test plots