r-help@stat.math.ethz.ch

Xin <jasonshi510 <at> hotmail.com> writes:

Dear All:

Then error messga there: initial value in 'vmmin' is not finite
In addition: There were 38 warnings (use warnings() to see them).

Could you give some advice please?

Thanks a lot!

Xin Shi

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A little more information (and an informative Subject: line)
would help.  A reproducible example (let us know how you're
calling optim(), and ideally show your data or a subsample
of it that produces the same problem --- see the posting guide).

A few ideas:

  - the 'vmmin' error message says that your starting values
are giving non-finite results -- this could be because some
of your x and y values are negative (which in your could
would lead to infinite values).  Bottom line: try your
objective function with your starting parameter values and
see what happens

  - you could use dnbinom(...,log=TRUE) if you wanted

  - you may need to be careful with constraining alpha, beta,
delta, as you could end up with negative means.