Re: Spline terms
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Re: Spline terms

On Thu, 8 Oct 1998, Chungui Qiao wrote:

> Hi there,
> I understand that if you want to fit a random spline row, you must fit a 
> fixed linear row in the model as well. So what is the difference between the 
> following two models:
yes thats right
We are considering changing this but at the moment spl() only fits the 
random component of a natural cubic spline. That is if there are p knot 
points (ie p rows) then spl() sets a random factor with p-2 levels. Thus 
p must be greater than 3. If you are interested I can send you the final 
version of the splines paper that we are presenting at Capetown in 
December, as a read paper. This explains things quite well.

> Model (1)        yield ~ lin(row) genotype !r spl(lin(row))
> Model (2)        yield ~ lin(row) genotype !r spl(row)
> I found in some of the wheat variety trials I analyzed, fitting Model (1) 
> caused a problem "Insufficient points for spl(lin(row))", while fitting 
> Model (2) worked well. Is this due to the lack of degree of freedom for 
> Model (1) and how is the degree of freedom estimated ? Could we just simply 
> use Model (2) in this case?
I am not entirely sure why spl(lin(row)) presents problems. ASREML 
should just examine the argument to spl() and form the matrix Z from the 
set of unique values in the argument

hope this helps
brian cullis

> > Thanks for your 
consideration. > 
> Chungui  
> Chungui Qiao
> School of Land and Food,
> Uni of QLD
> St Lucia 4072, QLD
> Ph: (07)33652859
> Fax:(07)33651177

      Brian Cullis                       Tel: 02 6938 1855
      NSW Agriculture                    Fax: 02 6938 1809
      Wagga Agricultural Institute     email:
      Pine Gully Rd
      WAGGA WAGGA  NSW 2650