I want to set up manually some knots locations in the gam function that uses a tensor product.
For example :
set.seed(0)
n <- 500
x <- runif(n)
z <- runif(n)
y <- runif(n)
gam(y ~ te(x, z), knots = list(x = c(0.2, 0.5, 0.8), y=c(0.2, 0.5, 0.8)))
But I have this error :
Error in smooth.construct.cr.smooth.spec(object$margin[[i]], dat, knt) :
number of supplied knots != k for a cr smooth
I tried to add a k value in the tensor, but the error is still the same How can I solve this ? Thank you for your help.
The knot locations you specify via knots and the number of basis functions k must be compatible. In your example, the defaults were used for k which IIRC is to have k = c(5,5) for a 2d tensor product.
If you want to use the knot locations you specified then you need to set k lower than this:
knots <- list(x = c(0.2, 0.5, 0.8), z = c(0.2, 0.5, 0.8))
gam(y ~ te(x, z, k = c(3,3)), method = "REML", knots = knots)