-Need help with function

Hello everyone,

I have a function here that I wrote but doesn't seem to work quite
right.  Attached is the code.  In the calib funcion under the for loop
Bt[i+2]<-(1-m)*Bt[i+1]+Rt[i]*Rerr-Ct[i+1] returns NA's for everything
after years 1983 and 1984.  However the code works when it reads
Bt[i+2]<-(1-m)*Bt[i+1]+Rt[i]*Rerr-Ct[i].  I don't quite understand why
since it should be calculating all of the necessary inputs prior to
calculating Bt[i+2].  Any help would be greatly appreciated.

Thanks

#Model parameters
B0<-75000000
m<-0.3
R0<-B0*m
z<-0.8
a<-B0/R0*(1-(z-0.2)/(0.8*z))
b<-(z-0.2)/(0.8*z*R0)
dat<-data.frame(years=seq(1983,2004),cobs=c(19032324,19032324,17531618,2
0533029,20298099,20793744,23519369,23131780,19922247,17274513,17034419,1
2448318,4551585,4226451,7183688,7407924,7538366,7336039,8869193,7902341,
6369089,6211886))
stdr<-runif(100,0,0.5)
stdc<-runif(100,0,0.5)
BC<-runif(1000,0,100)


#model calibration

calib<-function(x){
 v<-sample(stdr,1)
 cr<-sample(stdc,1)
 N<-rnorm(1)
 Bq<-sample(BC,1)
 Rerr<-exp(N*v-(v^2/2))
 Cerr<-exp(N*cr-(cr^2/2))
 Bt<-vector();Bt[1]=B0;Bt[2]=B0
 Rt<-vector()
 Ct<-vector()
 for (i in 1:length(x$years)){
 Ct[i]<-1/Bq*Bt[i]*Cerr
 Rt[i]<-Bt[i]/(a+b*Bt[i])
 Bt[i+2]<-(1-m)*Bt[i+1]+Rt[i]*Rerr-Ct[i+1]
 }
 out<-new.env()
 out$yr<-x$years[1:length(x$years)]
 out$Bt<-Bt[1:length(x$years)]
 out$Rt<-Rt[1:length(x$years)]
 out$Ct<-Ct[1:length(x$years)]
 out$stdr<-v
 out$stdc<-cr
 out$Bq<-Bq
 out$Rerr<-Rerr
 out$Cerr<-Cerr
 return(as.list(out))
 }
 test<-calib(dat)



Cameron Guenther, Ph.D.
Associate Research Scientist
FWC/FWRI, Marine Fisheries Research
100 8th Avenue S.E.
St. Petersburg, FL 33701
(727)896-8626 Ext. 4305
cameron.guenther at myfwc.com


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