>
> Dear Arthur,
>
> I am trying to fit three-way models, using US and FA structures. The
> following is an example. It works well with US (only a few seconds! great!
> With MIXED, it takes hours! While writing this, MIXED has not converged on
> the same data set).
>
> Unfortunately, I am having some problems with the FA starcture.
>
> Questions:
>
> (1) Do I need to specify !S2==1 also with the G.L and G.Y structures
> (G-matrices), as in the R-matrix structures? If I do, I get some strange
> error messages with some models. With US, the last variance parameter is
> fixed at 1, so it seems I should not be using "S2==1 with G structures. But
> why with the R-matrix and not with the G-matrix?
It is a matter of fixing the overall scale. Essentially the Variance
Structure is S2(R+ZGZ') .
If R is a correlation matrix (e.g. ARxAR as in the spatial analysis,
I as in a simple mixed model - say incomplete block analysis) then S2 is
needed. So the default for a univariate analysis at one site is to
estimate S2 and assume R is a correlation. I suppose ASREML could work it out
but it doesn't at the moment and the default is the most common case.
G is then parameterized in terms of Gammas (Variance ratios)
However, in your case R is a variance matrix 9it includes a scaling
parameter. The choice is then to fix S2 (at say 1 but it could be
any value) or to fix an element in R (which is possible). G is then
placed on the same scale. It is important then that G always include
a scale parameter.
>
> (2) When I replace the first US (R-matrix) by FA in the code below, ASREML
> aborts with the error message "AIGETR FA 2". How can this be fixed?
>
yield ~ mu !r L.G Y.G !f G mv
1 3 2 !step 0.01
L L !S2==1
Y Y !S2==1
G G US !GP !+10
2
1 2
1 1 2
1 1 1 2
First S2 should only be specified once
Secondly, The order of G (4) is not big enough to sustain 2 factors.
2 factor FA of 4 levels involves 12 parameters but a full US only has 10.
Since I overwrite the initial US with the FA parameters, there is
not enough room.
Thirdly, we hqve often had dificulty getting FA 2 and higher working
without using good starting values. So a better way of setting it up
is
G G FA !G5PZ4P5P !A !V2 !+15 # Assuming 5 levels
5*.7
5*.1
5*2
> (3) When I replace the second US by FA/FACV, thr program runs, but I get 2
> strange variances in the output:
>
> Variance 400 319 0.00000 0.00000 0.00 0 F
> Variance 400 319 0.00000 0.00000 0.00 0 F
>
> Funnily, this does not happen, if I replace (only) the third US by FA/FACV.
> What is wrong here?
These lines should not be printed.
ASREML reads in the 10 parameters for the US layout and then
reparameterizes to the 8 parameters of the FA1 layout. This leaves
2 unused positions which are set to zero. I'll look for the reason
they appear but the should not. Ignore them.
>
> (4) I thought, using !V2 on the FA structure, i.e.
>
> G 0 FACV !V2 !GP !+10 ,
>
> I would be fitting 2 factors, but I end up with only one term and the same
> fit as when not using !V2. What am I missing?
You need at least 5 levels in G to fit FA 2 as explained above.
I realise you couuld define an FA2 putting an appropriate constraint
to reduce the free parameters from 12 to 10 but I do not allow that
(probably even if you put the vectors in directly).
Arthur
> threeway
> Y 10
> L 10
> G 4
> yield
> threeway.dat !MAXIT 50
> yield ~ mu !r L.G Y.G !f G mv
> 1 3 2 !step 0.01
> L L !S2==1
> Y Y !S2==1
> G G US !GP !+10
> 2
> 1 2
> 1 1 2
> 1 1 1 2
> L.G 2
> L 0
> G 0 US !GP !+10
> 2
> 1 2
> 1 1 2
> 1 1 1 2
> Y.G 2
> Y 0
> G 0 US !GP !+10
> 2
> 1 2
> 1 1 2
> 1 1 1 2
<><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><>
Arthur Gilmour PhD mailto:Arthur.Gilmour@agric.nsw.gov.au
Senior Research Scientist (Biometrics) fax: <61> 2 6391 3899
NSW Agriculture <61> 2 6391 3922
Orange Agricultural Institute telephone work: <61> 2 6391 3815
Forest Rd, ORANGE, 2800, AUSTRALIA home: <61> 2 6362 0046
ASREML is still free by anonymous ftp from pub/aar on ftp.res.bbsrc.ac.uk
or point your web browser at ftp://ftp.res.bbsrc.ac.uk/pub/aar/
To join the asreml discussion list, send the message
subscribe
mailto:asreml-request@chiswick.anprod.CSIRO.au
To send messages to the list, mailto:asreml@chiswick.anprod.CSIRO.au
Asreml mailinglist archive: http://www.chiswick.anprod.csiro.au/lists/asreml
<> <> <> <> <> <> <>
"The Holy Scriptures are able to make you wise for salvation
through faith which is in Christ Jesus.
All Scripture is given by inspiration of God, and is profitable for
doctrine, for reproof, for correction, for instruction in righteousness,
That the man of God may be complete,
thoroughly equipped for every good work." II Timothy 3:15-17.
<><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><>
--
Asreml mailinglist archive: http://www.chiswick.anprod.csiro.au/lists/asreml