Available Commands
Once you have constructed an approximating or interpolating
thin-plate spline st with the aid of tpaps (or directly via stmak), you can use fnbrk to
obtain its parts or change its basic interval, fnval to evaluate it, fnplt to plot it, and fnder to
construct its two first partial derivatives, but no higher order derivatives
as they become infinite at the centers. This is just one indication
that the stform is quite different in nature from the other forms
in this toolbox, hence other fn... commands by
and large don't work with stforms. For example, it makes no sense
to use fnjmp, and fnmin or fnzeros only
work for univariate functions. It also makes no sense to use fnint on a function in stform since such
functions cannot be integrated in closed form. The command Ast
= fncmb(st,A) can
be used on st, provided A is
something that can be applied to the values of the function described
by st. For example, A might
be 'sin', in which case Ast is
the stform of the function whose coefficients are the sine of the
coefficients of st. In effect, Ast describes
the function obtained by composing A with st.
But, because of the singularities in the higher-order derivatives
of a thin-plate spline, there seems little point to make fndir or fntlr applicable
to such a st.
 | Properties of the stform | | Advanced Examples |  |
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