R/rvonmises.R

In Directional: A Collection of Functions for Directional Data Analysis

################################
#### Simulating from a von Mises distribution using the algorithm for
#### the von Mises-Fisher distribution
#### Tsagris Michail 2/2015
#### mtsagris@yahoo.gr
#### References: Wood ATA (1994)
#### Simulation of the von Mises Fisher distribution (Communications in Statistics-Simulation) and
#### Inderjit S. Dhillon and Suvrit Sra (2003)
#### Modeling Data using Directional Distributions (Technical report, The University of Texas at Austin)
################################
rvonmises <- function(n, m, k, rads = TRUE) {
 Rfast::rvonmises(n, m, k, rads)
}




# rvonmises <- function(n, m, k, rads = TRUE) {
#   ## n is the sample size
#   ## m is the mean angle expressed in radians or degrees
#   ## k is the concentration parameter
#   if ( !rads )  m <- m/180 * pi  ## turn the degrees into radians
#   mu <- c( cos(m), sin(m ))
#   if (k > 0) {  ## draw from a von Mises distribution
#     x <- rvmf(n, mu, k)  ## sample from the von Mises distribution
#     ## x is expressed in cartesian coordinates. We have to transform
#     ## the values into degrees or radians
#     u <- ( atan(x[, 2]/x[, 1]) + pi * I(x[, 1] < 0) ) %% (2 * pi)  ## u is in radians
#
#   } else  u <- runif(n, 0, 2 * pi)  ## draw from a von Mises distribution
#   if ( !rads )  u <- u * pi/180  ## should the data be in degrees?
#
#   u
# }