> I'm looking for a routine that can create a cubic spline fit from an > arbitrary set of points in 3 dimensions, represented by $(x,y,z,v)_i$ > (preferrably in a weighted least squares sense). > > For 2 dimensions (i.e. for surfaces with points $(x,y,v)_i$ )these > routines already exist. For example such a routine is given by NAGs > E02DAF.
Is it possible that you can call the 2-D function to calculate $(x,y,v)$ and call it again for $(z,0,v)$? Mathematically, it makes sense because you are dealing with linearly independant functions, ie. the value of the spline for $(z,0,v)$ should have ZERO effect on the values for $(x,y,v)$.
The only problems I can see for using this idea is if the functions require that the known values of $(x,y,v)$ are stored in a two-dimensional array instead of three one-dimensional array.
A better idea is if there is code to produce a one-dimensional spline $(x,v)$, call it three times, for $(x,v)$, $(y,v)$, $(z,v)$. This is also valid because x, y, and z are linearly independant, but it is a saivngs in work done by the computer because calculating $(z,0,v)$ involves a waste of work because the function will calculate a spline for $(0, v)$
> Secondly, has anybody experience with these kind of representations.
I've been toying with it, but I don't have any code that works completely, because I have been trying to code a spline funtion by myself.
-- _____________________________________________________________________ thomas delbert wilkinson 038 henday lister hall university of alberta If god were perfect, why did He create discontinuous functions? http://ugweb.cs.ualberta.ca/~wilkinso/