R help - Apr 2010 - Simulation problem.

Hi,
I have problem with simulating.
This is my task...

Suppose that there are N persons some of whom are sick with influenza. The
following assumptions are made:
* when a sick person meets a healthy one, the chance is á that the latter
will be infected
* all encounters are between two persons

Write a function which simulates this model for various values of
N (say, 10 000) and á (say, between 0.001 and 0.1). Monitor the
history of this process, assuming that one individual is infected at
the beginning.

The code is:
*
simulation <- function(number, prob){
cumulative.time <- 0
current.time <- 0
number.sick <- 1
while(number.sick<number){
current.time <- current.time + 1

meetings <- rhyper(nn=1, m=number.sick, n=number-number.sick, k=2)

if(meetings==1){
one.sick <- rbinom(n=1, size=1, prob)
if(one.sick==1){
cumulative.time <- c(cumulative.time, current.time)
number.sick <- number.sick + 1
}}}
cumulative.time
}

number <- 1000
prob <- .05
model <- simulate(number, prob)*

But than  add the assumption that *each infected person has a 0.01 chance
of recovering at each time unit*.... Do you have idea how to modify the code
?

Piotr Arendarski

	[[alternative HTML version deleted]]

This looks like homework.  If it is, you should really tell us along with what
your teacher's policy is on getting help over the internet is (and note that
many teachers monitor this list and can see if you are getting help).

You have done the first part yourself, much better than some who have tried to
get us to do the whole thing for them, so a possible hint:  the new problem
really has 3 groups, never sick, currently sick, and healed.  Just modify your
current code to allow for people to move from the currently sick to the healed
group.

-- 
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at imail.org
801.408.8111

> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of Piotr Arendarski
> Sent: Tuesday, April 13, 2010 4:27 PM
> To: r-help at r-project.org
> Subject: [R] Simulation problem.
> 
> Hi,
> I have problem with simulating.
> This is my task...
> 
> Suppose that there are N persons some of whom are sick with influenza.
> The
> following assumptions are made:
> * when a sick person meets a healthy one, the chance is ? that the
> latter
> will be infected
> * all encounters are between two persons
> 
> Write a function which simulates this model for various values of
> N (say, 10 000) and ? (say, between 0.001 and 0.1). Monitor the
> history of this process, assuming that one individual is infected at
> the beginning.
> 
> The code is:
> *
> simulation <- function(number, prob){
> cumulative.time <- 0
> current.time <- 0
> number.sick <- 1
> while(number.sick<number){
> current.time <- current.time + 1
> 
> meetings <- rhyper(nn=1, m=number.sick, n=number-number.sick, k=2)
> 
> if(meetings==1){
> one.sick <- rbinom(n=1, size=1, prob)
> if(one.sick==1){
> cumulative.time <- c(cumulative.time, current.time)
> number.sick <- number.sick + 1
> }}}
> cumulative.time
> }
> 
> number <- 1000
> prob <- .05
> model <- simulate(number, prob)*
> 
> But than  add the assumption that *each infected person has a 0.01
> chance
> of recovering at each time unit*.... Do you have idea how to modify the
> code
> ?
> 
> Piotr Arendarski
> 
> 	[[alternative HTML version deleted]]