R help - Feb 2013 - help with population matrix

Hi guys, I am a biologist and an R newbie, and I'm learning how to create a
simple population model.

So, I have a population matrix ("pop")of 30 age classes of female (1:4
are
non-breeders, 5:30 are breeders) which will be modelled for 100 years.
> pop <- matrix(0,30,100)
I then populate this matrix with 3 young adult females.
> pop[5, 1] <- 3
I then want to run this for 100 years, with stochasticity, to see how this
population does over time.
> for (y in 1:100)  {
>     pop[1,t+1] <- rbinom(1,colSums(pop[5:30, t]), b/2)
(I haven't filled these in but you don't need them, they all have
different
survival probabilities to the sexually-mature adults.)
>    pop[5, t+1] <- rbinom(1, pop[4, t], s2)
>    pop[6, t+1] <- rbinom(1, pop[5, t], s2)
.....
>    pop[30, t+1] <- rbinom(1, pop[29, t], s2)
}

So my question is: is there any way of populating this matrix without
having to explicitly write 30 lines of code? Because lines 5 - 30 are all
going to be the same, and yet even after 5 hours (literally) of web
searching and R manual reading I can't find a way to index the rows, which
seems to be what's needed here.

Any insight is welcome here, including a different way of modelling this
population.
Many thanks, Sam.

	[[alternative HTML version deleted]]

Currently your code does not seem to make any sense
===comments in line===
John Kane
Kingston ON Canada

> -----Original Message-----
> From: sf62 at st-andrews.ac.uk
> Sent: Mon, 18 Feb 2013 16:09:49 +0000
> To: r-help at r-project.org
> Subject: [R] help with population matrix
> 
> Hi guys, I am a biologist and an R newbie, and I'm learning how to
create
> a
> simple population model.
> 
> So, I have a population matrix ("pop")of 30 age classes of female
(1:4
> are
> non-breeders, 5:30 are breeders) which will be modelled for 100 years.
> 
>> pop <- matrix(0,30,100)
> 
> I then populate this matrix with 3 young adult females.
> 
>> pop[5, 1] <- 3
What is this expected to do?
> 
> I then want to run this for 100 years, with stochasticity, to see how
> this
> population does over time.
> 
>> for (y in 1:100)  {
>>     pop[1,t+1] <- rbinom(1,colSums(pop[5:30, t]), b/2)
> 
> (I haven't filled these in but you don't need them, they all have
> different
> survival probabilities to the sexually-mature adults.)
> 
>>    pop[5, t+1] <- rbinom(1, pop[4, t], s2)
>>    pop[6, t+1] <- rbinom(1, pop[5, t], s2)
> .....
>>    pop[30, t+1] <- rbinom(1, pop[29, t], s2)
> }
>
What is t , s2 b etc?


> So my question is: is there any way of populating this matrix without
> having to explicitly write 30 lines of code? Because lines 5 - 30 are all
> going to be the same, and yet even after 5 hours (literally) of web
> searching and R manual reading I can't find a way to index the rows,
> which
> seems to be what's needed here.
> 
> Any insight is welcome here, including a different way of modelling this
> population.
> Many thanks, Sam.
This may be one of the cases where it really is better to have some detailed
explanation of what you want rather than how to code it.

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