Messages from Usenet group comp.lang.idl-pvwave, compiled by Paulo Penteado
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?