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Differentiation in IDL [message #50650]

Mon, 16 October 2006 06:49

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

Folks,

OK, I'm missing something crucial here.

Suppose I have a sine function:

x = Findgen(360)
data = Sin(x * !dtor)
Plot, data

I know that d/dx(sin(x)) = cos(x). So, I would expect
a cosine looking curve if I differentiate the data above.

dx = DERIV(data)
OPlot, dx, Linestyle=2

The differentiated curve is almost a straight line! One
could argue that it might have the correct cosine *shape*
(squint your eyes a little bit), but the scale is vastly
different. How come?

Cheers,

David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Sepore ma de ni thui. ("Perhaps thou speakest truth.")

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