plotting the derivative of a splined/interpolated function

*To*: mathgroup at smc.vnet.net*Subject*: [mg50682] plotting the derivative of a splined/interpolated function*From*: atjurhs at 3drc.com (Todd Jurhs)*Date*: Fri, 17 Sep 2004 01:15:46 -0400 (EDT)*Sender*: owner-wri-mathgroup at wolfram.com

I'm attempting to read in a time ordered data file, create eiteher a splined or interpolated data function, take the derivative of the splined or interpolated function, and plot the resulting velocity curve. Here's what I've done: Reading the Data: dat2=Import["Documents/Rocketry_Files/MAWD_Flight_Data/bttb_i285r-2.txt","Table"] Using Interpolating Funtions: approx=Interpolation[dat2, InterpolationOrder\[Rule]5] InterpolatingFunction[{{0.,91.}},<>] checking that it works: approx[t]/.{t->11.2} 3993. and plotting the position curve: Plot[approx[t],{t,0,91}] I get a nice plot :) Doing the same thing with the SplineFit function: <<NumericalMath`SplineFit` approx2 = SplineFit[dat2, Cubic] SplineFunction[Cubic, {0., 1820.}, <>] checking that it works: approx2[11.2] {0.56,128.802} ParametricPlot[approx2[t], {t, 0, 1820}, PlotRange -> All, Compiled -> False] Again I get a nice plot :) Taking the derrivative of either the splined or interpolated functions also seems to work: dervie[t]=D[approx[t],t] InterpolatingFunction[{{0.,91.}},<>][t] dervie[t]/.{t->10.} 220. AND dervie2=D[approx2[t],t] (SplineFunction[Cubic, {0., 1820.}, <>])'[t] BUT I can't seem to plot either dervie or dervie2 with the standard Plot ParametricPlot commands So the question becomes is, how to I plot the derrivative of an interpolated or slpined function? Thanks for your help!