(Fwd) Re: priority of operators in the FOR ( ) statement

Dear All, 
I spent an entire evening in debugging a small, fairly simple 

in R - without success. It was my Guru in Bayesian Analysis, 

Fridtjof, who was able to diagonose the problem. He said that it 

a long time for him also to locate the problem. This program 
illustrates in some ways the shortcomings of the error messages 

***' # Bayesian Data Analysis ## 
source("M:/programming/Rfolder/Assignments/fortest.txt") 
 
# #Remove all objects from the workspace 
rm(list=ls()) 
# #We will also try to note the time that the program takes 
# #We will start the clock at starttime 
starttime <- proc.time()[3]; 
 

my.function<-function(x) { 
s2<-sqrt(2); 
if ((x>=0) & (x<s2)) return(x/2) 
else  
if ((x>=s2) & (x<1+s2)) return(0.2) 
else  
if ((x>=1+s2) & (x<1.5+s2)) return(0.6) 
else  
if ((x>1.5+s2) | (x<0)) return(0) 
} 

x<-rnorm(1000000) 
system.time(my1<-myfun(x,vec)) 

 
alphayx<-function(y,x) { 
fy<-my.function(y) 
fx<-my.function(x) 
fyx<-fy/fx 
# to account for 0/0 division 
if (is.na(fyx)) fyx<-0 
#fyx<-ifelse(is.na(fyx),0,fyx); 
alpha<-min(1,fyx) 
return(alpha) 
} 
 
sigma<-0.5; 
#nr is the number of iterations 
nr<-20 
x<-numeric(nr); 
x[1]<-1; 
t<-1:nr; 
 
for (i in 1:nr-1) { 
xi<-x[i]; 
yi<-rnorm(1,mean=xi,sd=sigma); 
ui<-runif(1,0,1); 
ualphai<-alphayx(yi,xi); 
xn<-ifelse(ui<=ualphai,yi,xi); 
x[i+1]<-xn; 
} 
 
plot(t,x,type="p") 
 
endtime<-proc.time()[3]; 
elapsedTime<-endtime-starttime; 
cat("Elapsed time is", elapsedTime, "seconds", "\n")