[R] An infinite recursion error please explain!

[Uwe Ligges]

On 23.07.2011 04:29, mousy0815 wrote:
> Probability<- function(N, f, w, b, y, t, q) {
> 	#N is the number of lymph nodes
> 	#f is the fraction of Dendritic cells (in the correct node) that have the
> antigen
> 	#w is time in terms of hours
> 	#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))
> 	#y is the number of time steps it takes to traverse the gap (8hr/y)
> 	#t is the number of time steps it takes to traverse a node. (24hours total
> -- so 24hr/t)
> 	#q is the length of the time step
> 	
> 		m<- ceiling(w/q)
> 		A<- 1/N
> 		B<- 1-A
> 		C<- 1-f
> 		D<- (((m+b-1)%%(y+t))+1)
> 		
> 	
>
> 		if (b<=t) {########starts inside node
> 		if (m<=(t-b)){return(B + A*(C^m))} # start&  end in first node		
> 		if (D<=t) { # we finish in a node
> 			a<- (B + A*(C^(t-b))) #first node
> 			b<- ((B + A*(C^t))^(floor((m+b)/(y+t))-1))  # intermediate nodes (if
> any)
> 			c<- (B + A*(C^D))  # last node
> 			return(a*b*c)
> 			} else {return(Probability(N, f, ((m*q)-q), b, y, t, q))} ## finish in a
> gap	
> 		} else {###### starts outside node
> 			if (m<=(y+t-b)) {return(1)} #also end in the gap
> 			if (D<=t) { #end in a node
> 				b<- ((B + A*(C^t))^(floor((m/(y+t)))))
> 				c<- (B + (A*(C^D)))
> 				return(b*c)
> 				} else {return(Probability(N, f, ((m*q)-q), b, y, t, q))} #outside node
> 		}
> 	}	
>
>
> This works for most values of 'w' (time):
>
>> Probability(100, 0.001, 1, 1, 20, 20, (10/60))
> [1] 0.9999401
>> Probability(100, 0.001, 2, 1, 20, 20, (10/60))
> [1] 0.9998807
>> Probability(100, 0.001, 3, 1, 20, 20, (10/60))
> [1] 0.9998215
>> Probability(100, 0.001, 4, 1, 20, 20, (10/60))
> Error: evaluation nested too deeply: infinite recursion /
> options(expressions=)?
>
> But once I get to w=4 I get an infinite recursion. I get that there is a
> recursion in my function but I'm not sure why it wouldn't work. After a
> certain point (D<=t) would be true.

Maybe that certain point is nested rather deeply in your recursion (if 
it actually exists, which I have not checked). If you change 
options(expressions) to allow for a deeper recursion you end in a 
protection stack overflow. Therefore it is obviously advisable to use an 
iterative approach here.

Best,
Uwe Ligges






> Any help, please?
>
> --
> View this message in context: http://r.789695.n4.nabble.com/An-infinite-recursion-error-please-explain-tp3688260p3688260.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.