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RE: st: RE: Problems in maximising a likelihood function
One source of weird bugs is if any of
your scalar names is interpretable as
a variable name. Using temporary names
for your scalars would fix that.
This is discussed for example in Tip
31 of Stata Journal 6(2).
> There may be a moral here, but that scalars
> are a disaster for holding constants and
> that temporary variables are better really
> cannot be inferred from the story you
> present. In essence, you assert that,
> but present no evidence. I suspect some
> other explanation for your problems, but
> I do not know what it is.
> Deepankar Basu
> > Nick,
> > There is a world of difference between scalars and
> temporary variables
> > (generated as -double-) at least in the context of -ml-
> > estimation. As I
> > discovered the hard way, after several days of labour.
> > When I had first written the program there were several mistakes. I
> > corrected them over many iterations, with help and advice from
> > statlisters. But, I also changed my temporary variables to
> > scalars, and
> > that was a disaster.
> > Because, when I had corrected everything else in the program, I was
> > still not getting convergence because of scalars. I had tried
> > everything
> > and was almost on the verge of giving up; then it struck me
> > as a passing
> > thought that maybe I should just try using temporary variables once
> > again. I did so and presto! There was convergence!
> > Moral of the story: never use scalars in -ml- estimation; use
> > temporary
> > variables (if you need them) and generate them as -double-.
> > And only as
> > -double-.
> > Deepankar
> > On Thu, 2006-06-15 at 21:48 +0100, Nick Cox wrote:
> > > Quite so. I spoke too soon on that detail.
> > >
> > > Nick
> > > firstname.lastname@example.org
> > >
> > > Deepankar Basu
> > >
> > > > But I cannot clean up the expression for the log likelihood
> > > > any further.
> > > > As I had said earlier, the log likelihood for each
> > > > observation is of the
> > > > following form: ln(a+b); where 'a' and 'b' are huge expressions
> > > > involving exponentials, etc. I don't see how I can
> simplify it any
> > > > further;
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