# R/sim_background.R In surveillance: Temporal and Spatio-Temporal Modeling and Monitoring of Epidemic Phenomena

#### Documented in sim.seasonalNoise

```###################################################
### chunk number 1:
###################################################

# 'sim.seasonalNoise' generates a cyclic model of a poisson distribution
# as background data for a simulated timevector.
#
# Parameters:
# A             - amplitude (range of sinus), default = 1
# alpha         - parameter to move along the y-axis
#                       (negative values not allowed)
#                       d.h alpha > = A, default = 1,
# beta          - regression coefficient, default = 0
# season        - factor to create seasonal moves
#                       (moves the curve along the x-axis), default = 0
# length                - number of weeks to model
# frequency     - factor to determine the oscillation-frequency, default = 1
# state        - if a state chain is given, it is weighted by the parameter K
#                       and influences mu
# K             - weight for outbreaks

sim.seasonalNoise <- function(A = 1, alpha = 1, beta = 0, phi = 0,
length, frequency = 1, state = NULL, K = 0){

t <- 1:length

# constant factor to transform weeks to the appropriate pi-value.
omega <- 2 * pi/ 52

# season moves the sin along the x-axis.
if(is.null(state)){ # no state chain
mu <- exp(A * sin( frequency * omega * (t + phi)) + alpha  + beta * t)
}
else{ # encounter the state chain
mu <- exp(A * sin( frequency * omega * (t + phi)) +
alpha  + beta * t +  K * state)
}

# create the noise as random numbers of the Poisson distribution
# with parameter mu
seasonalBackground <- rpois(length, mu) # get random numbers

result <- list(seasonalBackground = seasonalBackground, t = t,
mu = mu, A = A, alpha = alpha,
beta = beta, phi = phi,
length = length,
frequency = frequency, K = K)

class(result) = "seasonNoise"
return(result)
}
```

## Try the surveillance package in your browser

Any scripts or data that you put into this service are public.

surveillance documentation built on July 20, 2022, 1:06 a.m.