为什么我在mlogit（）中出现错误，但在我添加+0而不截取各个特定变量时却没有出现错误？

Question

我正在尝试使用mlogit分析一些数据。我收到一个错误消息： resolve.default（H，g [！fixed]）中的错误：系统在计算上是单数的：倒数条件编号= 1.18087e-27“

(choice~1|v1+v2+...vn, data, shape="long",alt.var="Mode",choice="Choice")

尽管，当我在公式的第二部分（单个特定变量）中添加+0时，因此不需要系数的截距，我也不会出错。

mlogit(choice~1|v1+v2+...vn+0, data, shape="long",alt.var="Mode",choice="Choice")

摘要如下所示：

Call:
mlogit(formula = Choice ~ 1 | +0 + fromSYR + fromNYC + fromALB + 
    DistSYR + DistNYC + DistALB + SafteyPersonal + SafteyTrainBus + 
    SafteyCarpool + SafteyTaxi + SafteySharedTaxi + PrivacyPersonal + 
    PrivacyTrainBus + PrivacyCarpool + PrivacyTaxi + PrivacySharedTaxi + 
    ConviniencePersonal + ConvinienceTrainBus + ConvinienceCarpool + 
    ConvinienceTaxi + ConvinienceSharedTaxi + TimePersonal + 
    TimeTrainBus + TimeCarpool + TimeTaxi + TimeSharedTaxi + 
    flightsYear + daysBreturn + luggage + ownVehicle + incomeB + 
    familySize + ageB + shuttleMaxPersonsB + payUticaSYR + payUticaALB, 
    data = Ta, method = "nr")

Frequencies of alternatives:
 Carpool Personal     Taxi TrainBus 
 0.31250  0.43750  0.21875  0.03125 

nr method
20 iterations, 0h:0m:0s 
g'(-H)^-1g = 7.46E-07 
gradient close to zero 

Coefficients :

.....

Log-Likelihood: -2.7444e-07