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
Can someone tell me why this is happening??
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