[R-sig-ME] GAMM convergence issue with temporal covariate

[Philippi, Tom]

Is your range tidal height at the same location at the time of sampling
(time & day), or variation among sites in elevation above some datum at the
(same) time of sampling?  Or does it vary by day but not by time?

If the former, given the predictable way that the tide cycle shifts from
one day to the next, for some times of the year you're going to have a
tough time separating out an effect of range from smoothed effects of day
and time.  If you need to visualize this, pull the NOAA 6 minute tidal
predictions from somewhere near your site (I can send R code to do this).
Or, plot a simple heatmap of your data:
    lattice::levelplot(range~day+time,data=dsn)

Also, be careful with your cyclic fit on time of day.
    s(time,bs="cc")
If your time values are not evenly spaced (e.g., full 0:24) you are likely
to need to specify knots to let gamm know that 0 and 24 are the ends to
match.  My first guess would be that you need:
   knots=list(time=c(0,24))
but I don't know your data, so your mileage will vary.

Tom 2

On Wed, Oct 14, 2015 at 10:19 AM, Highland Statistics Ltd <
highstat at highstat.com> wrote:

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> ------------------------------
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> Message: 2
> Date: Mon, 12 Oct 2015 12:13:44 -0700
> From: "Hannah L. Linder" <lindeh at uw.edu>
> To: r-sig-mixed-models at r-project.org
> Subject: [R-sig-ME] GAMM convergence issue with temporal covariate
> Message-ID:
>         <CAF0=RbauKGU3JOsPxBkuka=
> MBZZU0rZNkAyYt_or4p1h25wmBQ at mail.gmail.com>
> Content-Type: text/plain; charset="UTF-8"
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> Hello,
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> I am working with a fairly simple model:
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> gamm(sv~s(day,bs="cr")+range+s(time,bs="cc"),correlation=corARMA(p=2,q=2)
>
> In which day is Julian Day over one month, range is tidal range, and time
> is coded 1-24 for hour of day.
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> I continually have singularity convergence problems with this model (the
> error is:  nlminb
> problem, convergence error code = 1 message = false convergence (8).
>
> Increasing iterations does not help. When I run msVerbose I notice that
> "day" covariate output values (there are two but I'm not completely sure
> how to interpret them) keep increasing until the convergence errors occur.
> I have also noticed that setting k=5 for the "day" covariate does not help
> the convergence problem, but k=9 does (the default is 10) or k =20. I would
> greatly appreciate any advice or recommendations on what may be causing the
> problem.
>
> Thank-you very much,
> Hannah
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> Hannah,
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> CorARMA(p = 2, q = 2) is not an easy one for the optimisation routine. Try
> simplifying it.
> Additionally...the ARMA residual correlation structure may be competing
> with the time smoothers.
> You could try to use fixed values for the ARMA parameters.
>
>
> Alain Zuur
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