[R] “Error in if (abs(x - oldx) < ftol)” when using “lognormal” distribution in mixed logit

[Dong Wang]

Hi Henric,

Thank you for your reply! It really helps. I should have noticed this
earlier. I don't have a negative input, the error is because our survey
allowed people to choose neither of the choices we gave, so we added a
choice "Neither" with both deductible and premium being 0, which caused
this problem. I tried to delete the "0" entries just now and it worked! I
think I need to find a way do deal with the "Neither" choice in another way.

Thank you so much and have a nice weekend!

Best, Dong

On Fri, Jul 24, 2015 at 7:16 AM, Henric Winell <nilsson.henric at gmail.com>
wrote:

> Den 2015-07-24 kl. 00:33, skrev Dera:
>
>  Hi, I have a question about how to use the mlogit package in R to do
>> analysis
>> of discrete choice survey data. Our survey is about asking people to
>> choose
>> from different insurance policies(with two attributes of deductible and
>> premium).
>>
>> The code I used to fit mixed logit is:
>>
>>
>> [1] ml <- mlogit.data (mydata, choice="choice", shape = "wide", id =
>> "individual",
>>                 opposite =c ('deductible', 'premium'),varying = 5:10)
>>
>> [2] ml.w5 <- mlogit (choice~deductible+premium|0, ml, panel = TRUE,
>>               rpar = c(deductible='ln', premium='ln'),
>>               R = 100, halton = NA, print.level=0)
>>
>> I try to use lognormal because we hope the coefficients for both
>> deductible
>> and premium are negative. And I use "opposite" in [1] to reverse the sign
>> because lognormal is always positive.
>>
>> But I always get the error warning:
>>
>> "Error in if (abs(x - oldx) < ftol) { : missing value where TRUE/FALSE
>> needed
>> In addition: Warning message: In log(start[ln]) : NaNs produced"
>> I double check the data and am sure there isn't any missing data. And if I
>> change the lognormal "ln" to "n" or "cn", it will work without any
>> warning.
>>
>> Does anyone know how to deal with this? Thank you for your help.
>>
>
> I've never used the 'mlogit' package but that error message has likely
> nothing to do with missingness in your data.
>
> The error message is pretty clear: for some reason 'if (abs(x - oldx) <
> ftol)', which looks like a check for convergence, doesn't evaluate to TRUE
> or FALSE as expected.  Perhaps due to the warning message about problems
> with NaN in the starting values?  Have you checked your data? That warning
> message is typical for when you try to take logs of a negative number:
>
> > log(-1)
> [1] NaN
> Warning message:
> In log(-1) : NaNs produced
>
> Unless this helps you identify the problem, we need a (preferably small)
> reproducible example demonstrating the issue to be able to provide further
> help.
>
> BTW, have you asked the package maintainer (as per the posting guide)?
>
>
> Henric Winell
>
>
>
>
>>
>>
>> --
>> View this message in context:
>> http://r.789695.n4.nabble.com/Error-in-if-abs-x-oldx-ftol-when-using-lognormal-distribution-in-mixed-logit-tp4710284.html
>> Sent from the R help mailing list archive at Nabble.com.
>>
>> ______________________________________________
>> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide
>> http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>>
>>
>

	[[alternative HTML version deleted]]