[SciPy-user] Finding min/max of a B-Spline
Willi Richert
w.richert@gmx....
Fri Aug 17 13:21:41 CDT 2007
Hi,
I have a sequence of n-dim points for which I approximate a spline via splrep
and splev. For splev I can specify der=1 to get the first derivative
evaluated. And there is sproot, which finds the roots of the originially
created spline. However, with these methods I cannot find the roots of the
first derivative to get the minima and maxima of the spline. How can that be
achieved?
As an example take the 2-dim case (scipy 0.5.2):
=========================
from pylab import *
from scipy.interpolate import splrep, splev, sproot, spalde
import pylab
x=linspace(0,2*pi, 100)
y=sin(linspace(0,2*pi, 100))
rep=splrep(x, y, k=3, s=1)
ynew = splev(x, rep)
raw_points = plot(x,y)
spline_points = plot(x, ynew)
y_der = splev(x, rep, der=1)
p_der = plot(x, y_der)
# x,y_der now contain the evaluated data for the first derivative.
# The only chance to get the root would be to again fit a polynomial
# to the data. However, that might be overkill. What else?
legend([raw_points, spline_points, p_der], \
["raw", "spline", "derivative"], "upper left")
grid()
show()
=========================
Best regards,
wr
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