On On, 2005-11-23, 05:43, Tomas skrev:> Dear R-hep,
> I'm trying to get the first derivative of a smooth from a gam
> model like:
> model<-gam(y~s(x,bs="cr", k=5)+z) and need the derivative:
ds(x)/dx. Since
> coef(model) give me all the parameters, including the parameters of the
> basis, I just need the 1st derivative of the basis s(x).1, s(x).2, s(x).3,
> s(x).4. If the basis were generated with the function spline.des() from
> the
> spline library I would be able to get the derivative of the basis and
> would
> be pretty much done. (spline.des() has the option of computing 1st
> derivative)
>
> The difficulty I'm having is that I can't get how the basis were
> generated.
> If I define an "s" object like:
object<-s(x,bs="cr",k=5) and use
> smooth.construct() to generate the basis, it gives 5 basis but the gam
> object "model" gives only 4 s(x).i elements. It generalizes for
different
Try
> model2 <- gam(y ~ s(x, bs = "cr", k = 5) + z, control
gam.control(absorb.cons = FALSE))
> coef(model2)
(Intercept) z s(x).1 s(x).2 s(x).3 s(x).4 s(x).5
43.675698 -2.685739 -43.305376 -34.325047 -14.015483 20.155349 71.490557
See ?gam.control
HTH,
Henric
> values of k. See the example:
>
> library(mgcv)
> y<-c(1,5,6,12,13,14,45,42,56,68,89,120)
> z<-c(rep(0,5),rep(1,7))
> x<-c(seq(1:12))
> data<-data.frame(y,x,z)
>
> model<-gam(y~s(x,bs="cr", k=5)+z)
>
> object<-s(x,bs="cr", k=5)
> basis<-smooth.construct(object,data,knots=NULL)
>
> summary(model)
> .
> .
> .
> Parametric coefficients:
> Estimate Std. Error t value Pr(>|t|)
> (Intercept) 43.676 5.492 7.953 6.66e-05 ***
> z -2.686 9.041 -0.297 0.775
> ---
> Signif. codes: 0 '***' 0.001 '**' 0.01 '*' 0.05
'.' 0.1 ' ' 1
>
> Approximate significance of smooth terms:
> edf Est.rank F p-value
> s(x) 2.53 4.00 35.18 6.48e-05 ***
>
> coef(model)
> (Intercept) z s(x).1 s(x).2 s(x).3 s(x).4
> 43.6756983 -2.6857394 -20.9429503 -0.6333857 33.5374463 84.8726537
>
> dim(basis$X)
> [1] 12 5
>
> #Here are the basis
> basis$X
>
> [,1] [,2] [,3] [,4] [,5]
> [1,] 1.000000000 0.00000000 0.00000000 0.00000000 0.000000000
> [2,] 0.551840721 0.55522164 -0.13523666 0.03380917 -0.005634861
> [3,] 0.180959536 0.93527960 -0.14682838 0.03670709 -0.006117849
> [4,] -0.035821616 0.96624450 0.08768917 -0.02173446 0.003622411
> [5,] -0.076875604 0.62353762 0.54792315 -0.11350220 0.018917033
> [6,] -0.027771815 0.17264141 0.93603091 -0.09708061 0.016180101
> [7,] 0.016180101 -0.09708061 0.93603091 0.17264141 -0.027771815
> [8,] 0.018917033 -0.11350220 0.54792315 0.62353762 -0.076875604
> [9,] 0.003622411 -0.02173446 0.08768917 0.96624450 -0.035821616
> [10,] -0.006117849 0.03670709 -0.14682838 0.93527960 0.180959536
> [11,] -0.005634861 0.03380917 -0.13523666 0.55522164 0.551840721
> [12,] 0.000000000 0.00000000 0.00000000 0.00000000 1.000000000
>
> #and their knots
>
> basis$xp
> [1] 1.00 3.75 6.50 9.25 12.00
>
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