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Re: Slope of a graph [message #66322] Sat, 02 May 2009 05:12
jameskuyper is currently offline  jameskuyper
Messages: 79
Registered: October 2007
Member
d.poreh@gmail.com wrote:
> Folks
> I have an elevation distance plot (elevation-distance) in 2D and I
> want to calculate slope of this graph. For instance:
> DL> x=findgen(100)
> IDL> y=exp(-x)
> I need to calculate the slope of this graph in 100 points
> (corresponding to x). I tested DERIV function but seem shows incorrect
> results! In our example for low x we have high slope and for high x
> slopes are decreasing.

The slope of exp(-x) is -exp(-x), which start out with a value -1 at
x=0, and gets smaller for large x. With a spacing of 1 you can't get
very accurate values for the derivative using DERIV, but it should show
the same pattern. Is that what you are seeing?

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