我已经成功运行了以下两个嵌套的logit模型：
summary(mlogit(Response ~ 1 | Age + Sex + Income + Educatio + HomeLoca
+ CarOwn + CarHouse + LTimePT + LTimeCar + UmwFrei1 + DistPT1 + FrqInfo1Neu| Cost + Time + WalkTime, data =TM6, nests = list(convent = c("OwnCar","PT"), pooling = c("PoolPass","PoolDriv"))))
summary(mlogit(Response ~ 1 | Age + Sex + Income + Educatio + HomeLoca + CarOwn + CarHouse + LTimePT + LTimeCar + UmwFrei1 + DistPT1 + FrqInfo1Neu| Cost + Time + WalkTime, data =TM6, nests = list(beingDriven = c("PT","PoolPass"), Drive = c("OwnCar","PoolDriv"))))
但是，接下来的三个嵌套logit模型不起作用：
summary(mlogit(Response ~ 1 | Age + Sex + Income + Educatio + HomeLoca + CarOwn + CarHouse + LTimePT + LTimeCar + UmwFrei1 + DistPT1 + FrqInfo1Neu| Cost + Time + WalkTime, data =TM6, unscaled = TRUE, nests = list(PTT = "PT", Cars = c("OwnCar","PoolDriv", "PoolPass"))))
summary(mlogit(Response ~ 1 | Age + Sex + Income + Educatio + HomeLoca + CarOwn + CarHouse + LTimePT + LTimeCar + UmwFrei1 + DistPT1 + FrqInfo1Neu| Cost + Time + WalkTime, data =TM6, unscaled = TRUE, nests = list(OwnCar = "OwnCar", Else = c("PT","PoolDriv", "PoolPass"))))
summary(mlogit(Response ~ 1 | Age + Sex + Income + Educatio + HomeLoca + CarOwn + CarHouse + LTimePT + LTimeCar + UmwFrei1 + DistPT1 + FrqInfo1Neu| Cost + Time + WalkTime, data =TM6, unscaled = TRUE, nests = list(PTT = "PT", OwnCar = "OwnCar", Pool = c("PoolDriv", "PoolPass"))))
在这里，我遇到以下错误：
Error in solve.default(crossprod(attr(x, "gradi")[, !fixed])) :
system is computationally singular: reciprocal condition number = 8.23452e-21
mlogit软件包（https://cran.r-project.org/web/packages/mlogit/mlogit.pdf）上有更新。 该语法去年有效，但现在却提供了错误。有人知道我必须更改吗？
感谢您的帮助。谢谢！