Do you know about Fourier analysis?

http://en.wikipedia.org/wiki/Fourier_transform

Thanks,

Yes, I know about the FFT... at least in theory.

Perhaps I should look at it some more.

What I'm actually looking at is the Temperature Trends. In particular, 1997/1998 to present.

[attachment=14120]

As I noted from the sine curve above, one can obviously diddle with the end-points to prove anything that one wants.

Visually looking at the graph, it appears to have no significant trend.

But, when I plot the trend line, it invariably gives me a slight positive slope [

]

What I noticed was that the temperatures from 1999 to 2002 and 2008 to 2010 seem to increase in a sawtooth pattern, with a sharp downswing, and a gradual upswing, thus weighting more negative towards the early years, and more positive towards the later years.

And, what I was able to demonstrate with the stylized sawtooth pattern is that it will cause an upward trend in the trend line in most cases except when one begins with a peak and ends with a valley.

If I was looking at something with a slope of 1:2 or so... I really wouldn't care much about a fractional difference. But, with a nearly flat slope, it makes a huge difference. [xx(]

Anyway, it doesn't seem like a FFT type of function, but perhaps it will give me additional analysis tools and it certainly is something that I need to understand better.