On Jul 10, 2011, at 9:09 PM, mousy0815 wrote:
> I have the following code to determine the probability of a t-cell
> encountering an antigen after "m" steps.
>
> probability <- function(N, f, m, b, x, t) { #using ifelse instead of
> if/else
> #N is the number of lymph nodes
> #f is the fraction of Dendritic cells (in the correct node) that
> have the
> antigen
> #m is the number of time steps
> #b is the starting position (somewhere in the node or somewhere in
> the gap
> between nodes. It is a number between 1 and (x+t))
> #x is the number of time steps it takes to traverse the gap
> #t is the number of time steps it takes to traverse a node.
> A <- 1/N
> B <- 1-A
> C <- 1-f
> D <- (((m+b-1)%%(x+t))+1)
>
> ifelse(b<=t, ########starts inside node
> ifelse( (m<=(t-b)),
> return(B + A*(C^m)), # start & end in first node
> ifelse (D<=t, # we finish in a node
> return((B + A*(C^(t-b)))*((B + A*(C^t))^(floor(m/(x
> +t))-1))*(B +
> A*(C^D))),
> probability(N, f, (m-1), b, x, t)
> )
> ),
> ifelse( ########starts outside node
> m<=(x+t-b),
> return(1), #also end in the gap,
> ifelse (
> (D<=t), #end in a node
> (return(((B + A*(C^t))^(floor((m/(x+t)))))*(B + (A*(C^D))))),
> probability(N, f, (m-1), b, x, t)#outside node
> )
> )
> )
> }
>
> But I do:
>> m<- c(1:3)
>> probability(10, 0.1, m, 3, 4, 5)
> 0.9900000 0.9810000 0.9729000
>
> but if you do each number separately you get
>> probability(10, 0.1, 1, 3, 4, 5)
> 0.99
>> probability(10, 0.1, 2, 3, 4, 5)
> 0.981
>> probability(10, 0.1, 3, 3, 4, 5)
> 0.981
Your function is probably not fully vectorized. Try comparing with
sapply(1:3, function(x) probability( m =x, N=0.1, f=3, b=3, x=4,
t=5) )
--
David.>
> Can someone tell me why this is happening??
>
> --
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> Sent from the R help mailing list archive at Nabble.com.
>
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> and provide commented, minimal, self-contained, reproducible code.
David Winsemius, MD
West Hartford, CT