R中拟合模型的时候出现下面的情况，请问大神们怎么破

> Hawaii=read.table("Hawaii.txt",header = TRUE) > Birds=c(Hawaii$Stilt.Oahu,Hawaii$Stilt.Maui, + Hawaii$Coot.Oahu,Hawaii$Coot.Maui) > Time=rep(Hawaii$Year,4) > Rain=rep(Hawaii$Rainfall,4) > ID=factor(rep(c("Stilt.Oahu","Stilt.Maui","Coot.Oahu","Coot.Maui"), + each=length(Hawaii$Year))) > library(lattice) > xyplot(Birds~Time|ID,col=1) > library(mgcv) > BM1=gamm(Birds~Rain+ID+ + s(Time,by=as.numeric(ID=="Stilt.Oahu"))+ + s(Time,by=as.numeric(ID=="Stilt.Maui"))+ + s(Time,by=as.numeric(ID=="Coot.Oahu"))+ + s(Time,by=as.numeric(ID=="Coot.Maui")), + na.action=na.omit, + weights = varIdent(form = ~1|ID)) Error in MEestimate(lmeSt, grps) : Singularity in backsolve at level 0, block 1

> Hawaii=read.table("Hawaii.txt",header = TRUE) > Birds=c(Hawaii$Stilt.Oahu,Hawaii$Stilt.Maui, Hawaii$Coot.Oahu,Hawaii$Coot.Maui) > Time=rep(Hawaii$Year,4) > Rain=rep(Hawaii$Rainfall,4) > ID=factor(rep(c("Stilt.Oahu","Stilt.Maui","Coot.Oahu","Coot.Maui"), each=length(Hawaii$Year))) > library(lattice) > xyplot(Birds~Time|ID,col=1) > library(mgcv) > BM1=gamm(Birds~Rain+ID+ s(Time,by=as.numeric(ID=="Stilt.Oahu"))+ s(Time,by=as.numeric(ID=="Stilt.Maui"))+ s(Time,by=as.numeric(ID=="Coot.Oahu"))+ s(Time,by=as.numeric(ID=="Coot.Maui")), na.action=na.omit, weights = varIdent(form = ~1|ID)) 出现这样的错误 Error in MEestimate(lmeSt, grps) : Singularity in backsolve at level 0, block 1

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