which are the ways to do extrapolation?

I just wanted to know which are the best ways to do extrapolation. My data does not monotonously increase or decrease, so maybe interp functions won't work.

P.S please don't give me the Mark Twain quote!!

[Matt J]

The Mark Twain quote? What did Mark Twain ever have to say about extrapolation?

[Walter Roberson]

http://www.lhup.edu/~dsimanek/twain.htm

[Walter Roberson]

There are no "best ways" to do extrapolation except those that depend upon good models of the data being extrapolated.

Given any finite set of data points, there are an infinite number of functions that pass exactly through those data points. One would be tempted to say that there are even more that pass "closely" through the data points (reflecting measurement error), but of course infinity by another name would still smell as an awful lot of sweat to get to the end of.