Roger Hui wrote: > Sorry, I can not resist. The example is so short that even small > reductions are significant, and there are a couple: > - the parens are redundant > - x and y can be used instead of x. and y. (J6.01) > > Thus: > lagint=:13 : 'y.%. (x.^/i.#x.)' > > lagint=:13 : 'y%.x^/i.#x' >
Fair enough. In my defence, I wrote the response at 6am, and don't have J601 on my default computer (which runs Red Hat 8). I also understand that this will give exact results on integers with extended precision. All that I am doing is solving (V x)a=y for a, where V x is the Vandermonde matrix of x. As Roger has pointed out, this is useful in other contexts. The phrase I gave is suitable for casual use: you can do it a lot more efficiently than using matrix inversion. A particular case of this problem leads to the fast Fourier transform. If you are actually using Lagrange interpolation for large numbers of points, you probably should be looking at B-spline interpolation instead. Best wishes, John ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
