There is a trade-off between generality and speed.
Our goal is to develop software for general spline models.
Thus all functions in `ASSIST` require at least
flops. For some special spline models such
as polynomial splines, software exist which only require
flops. For example, the `smooth.spline` function
in S should be used to fit simple cubic spline models.

Fitting complicated smoothing spline models such as SS ANOVA
models with multiple smoothing parameters and SNMMs
are computationally intensive. For large data sets, it may
take hours and/or exhaust memory. Certain tricks in S are
helpful. For example, for kernels not available in our
library, it is more efficient to write functions in
lower languages such as C or Fortran and then load them
into S. Vectorization is also important. For large
data sets, one may re-set `memory` and `object.size`
arguments in the S function `options()` to increase
memory and object size. Control parameters such as the
number of iterations and convergence criteria can be
reset to save time.

Functions using iterative procedures such as `nnr`,
`snr` and `snm` may fail to converge within
the prespecified number of iterations. In these cases
convergence may be achieved with modifications of
some of the following arguments: initial values,
convergence criteria, method for estimating smoothing
parameters and number of iterations.

Some reproducing kernels in `ASSIST` library have
restricted domains (see Section 2). Thus it is important to
check whether the domain of a `rk` function coincides
with the range of a covariate. Otherwise, transformations
should be made or the `scale=T` should be used.
We recommend the first option.

The `nlme` library (version 3.0 or later)
is required for the `ssr` and
`nnr` functions when a unknown variance-covariance
structure is involved, and for the `slm`, `snr`
and `snm` functions. The `nlme` library in the
standard libraries, if available, may be loaded using

library(NLME,first=T)The

dyn.load("/home/nlme/NLME_l.o")We have used the same methods and notations as in