A matrix with the compositional data. No zero values are allowed.
nterms
The number of terms to include in the final model.
type
Either "alr" or "log" corresponding to the additive log-ratio transformation or the simple
logarithm applied to the compositional data.
xnew
If you have new data use it, otherwise leave it NULL.
Value
A list includign:
runtime
The runtime of the regression.
mod
The produced model as returned by the function "ppr".
est
The fitted values of xnew if xnew is not NULL.
Details
This is the standard projection pursuit. See the built-in function "ppr" for more details.
When the data are transformed with the additive log-ratio transformation this is close
in spirit to the log-contrast regression.
References
Friedman, J. H. and Stuetzle, W. (1981). Projection pursuit regression. Journal of the American
Statistical Association, 76, 817-823. doi: 10.2307/2287576.