R help - Mar 2003 - transition matrix problem

I'm having trouble using some fairly simple code to change the entries
in a vector (x - the numbers 0-5) according to a simple transition
matrix that I've called p.dry.  


the error message I get is 
"no finite arguments to min; returning Inf"

Any suggestions as to where I'm going wrong greatly appreciated. Sorry
the message is lengthy!

cheers
Nick


The code is 

p.trans<-matrix(c(1,0,0,0,0,0,0.7,0.3,0,0,0,0,0,0.6,0.4,0,0,0,0,0,0.5,0.5,0,0,0,0,0,0.4,0.6,0,0,0,0,0,0.3,0.7),6,6)

x<-ceiling(runif(100,0,5))

trans<-function(x) {
x.new<-vector(,length(x))
for (i in 1:length(x)) {
if (x[i]==0) x.new[i]<-0
else
cump<-(cumsum(p.trans[,(x[i]+1)])) # +1 b.c p.trans[,1] relates to
min(x)==0
names(cump)<-c("0","1","2","3","4","5")
rand<-ceiling(runif(1,0,100))
x.new[i]<-min(as.integer(names(cump[rand<(cump*100)])))
}
return(x,x.new)
}


Basically, in the transition matrix, the columns represent the current
cell entry in the vector (e.g. column 1 represents 0 (in the vector),
and the rows in the matrix are the possible transition states.  Hence,
cell entries in the transition matrix are the probabilities associated
with each transition.

The code works on the cumulative distribution of the relevant column of
the transition matrix, which is determined by the current cell value in
x.

-- 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Dr Nick Bond				 
Department of Biological Sciences 	 
Monash University (Clayton Campus)
Victoria, Australia, 3800
Ph: +61 3 9905 5606	Fax: +61 3 9905 5613
Email:   Nick.Bond at sci.monash.edu.au
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Nick  -

Ask yourself what happens in  min(as.integer(names(cump[rand<(cump*100)])))
when the random number happens to be larger than the first entry in the
relevant column of p.trans.  How many elements in the comparison are true ?

In that case, I think you are taking the minimum of zero elements, and the
error message is quite correct.

-  tom blackwell  -  u michigan medical school  -  ann arbor  -


On Tue, 4 Mar 2003, Nick Bond wrote:
> I'm having trouble using some fairly simple code to change the entries
> in a vector (x - the numbers 0-5) according to a simple transition
> matrix that I've called p.dry.
>
> the error message I get is  "no finite arguments to min; returning
Inf"
>
> The code is
>
>
p.trans<-matrix(c(1,0,0,0,0,0,0.7,0.3,0,0,0,0,0,0.6,0.4,0,0,0,0,0,0.5,0.5,0,0,0,0,0,0.4,0.6,0,0,0,0,0,0.3,0.7),6,6)
>
> x<-ceiling(runif(100,0,5))
>
> trans<-function(x) {
> x.new<-vector(,length(x))
> for (i in 1:length(x)) {
> if (x[i]==0) x.new[i]<-0
> else
> cump<-(cumsum(p.trans[,(x[i]+1)])) # +1 b.c p.trans[,1] relates to
> min(x)==0
>
names(cump)<-c("0","1","2","3","4","5")
> rand<-ceiling(runif(1,0,100))
> x.new[i]<-min(as.integer(names(cump[rand<(cump*100)])))
> }
> return(x,x.new)
> }
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> Dr Nick Bond
> Department of Biological Sciences
> Monash University (Clayton Campus)
> Victoria, Australia, 3800
> Ph: +61 3 9905 5606	Fax: +61 3 9905 5613
> Email:   Nick.Bond at sci.monash.edu.au
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~