First derivative of interpolated spline
- To: mathgroup at smc.vnet.net
- Subject: [mg25221] First derivative of interpolated spline
- From: Juerg Tschirren <jtschirr at engineering.uiowa.edu>
- Date: Fri, 15 Sep 2000 02:21:53 -0400 (EDT)
- Organization: University of Iowa
- Sender: owner-wri-mathgroup at wolfram.com
I am interpolating a cubic spline through a list with pairs of real
numbers with the following command sequence:
<<NumericalMath`SplineFit`
data = Import["data.dat", "Table"];
spline = SplineFit[data, Cubic]
ParametricPlot[spline[u], {u,0,301}, PlotRange->All, Compiled->False]
The file data.dat contains 300 numberpairs (real numbers), which results
in
data = {{0, 0}, {1, 55}, {2, 42}, {3, 52}, {4, 51}, ..., {300, 9}, {301,
0}}. The resulting plot looks like expected. Now I would like to
calculate the first derivative of the spline function and plot it. All
my attempts to do so failed (with the D and the Derivative function).
For example
ParametricPlot[D[spline[u],u], {u,0,301}, PlotRange->All,
Compiled->False]
results in messages like
General::ivar: 0.0000125417 is not a valid variable.
ParametricPlot::pptr:
D[spline[u], u] does not evaluate to a pair of real numbers at u =
0.0000125417.
What's wrong? Can anybody tell me how to do that?
Thanks
Juerg