[SciPy-User] 1-d Interpolation of unevenly spaced data

[Dybbroe Adam]

Thanks for the kind and useful help.
I am using the InterpolatedUnivariateSpline now, after having sorted the data and removed for duplicates.
-Adam


On 2011-02-02 01:09, Charles R Harris wrote: 



	On Tue, Feb 1, 2011 at 4:23 PM, Dybbroe Adam <Adam.Dybbroe at smhi.se> wrote:
	

		Thanks.
		Ok, I have stored my data in an npz-file (attached).
		You should be able to run the following code (with the npz file in the
		same directory from where you run):
		
		     import numpy as np
		     outfile = './ipol_test_arrays.npz'
		
		     from scipy.interpolate import splrep, splev
		
		     # Load data and try do the spline interpolation:
		     npzfile = np.load(outfile)
		     wvl = npzfile['wvl']
		     resp = npzfile['resp']
		     xspl = np.linspace(wvl[0], wvl[-1], 300) 


		     tck = splrep(wvl, resp)
		     resp_ipol = splev(xspl, tck)
		
		
		
		Here is what I get:
		
		In [1]: run scipy_ipol_test_ext.py
		---------------------------------------------------------------------------
		ValueError                                Traceback (most recent call last)
		
		/local_disk/laptop/NowcastingSaf/radiationStuff/test/scipy_ipol_test_ext.py
		in <module>()
		      14     xspl = np.linspace(wvl[0], wvl[-1], 300)
		      15
		---> 16     tck = splrep(wvl, resp)
		      17     resp_ipol = splev(xspl, tck)
		      18
		
		/home/a000680/usr/lib64/python2.5/site-packages/scipy/interpolate/fitpack.pyc
		in splrep(x, y, w, xb, xe, k, task, s, t, full_output, per, quiet)
		     416         else:
		     417             try:
		--> 418                 raise _iermess[ier][1],_iermess[ier][0]
		     419             except KeyError:
		     420                 raise _iermess['unknown'][1],_iermess['unknown'][0]
		
		ValueError:     Error on input data
		WARNING: Failure executing file: <scipy_ipol_test_ext.py>
		
		
		


	The contents of wvl need to be in sorted order, wvl[16] is out of order. Further, I wouldn't recommend letting splrep choose the knot points. A plain old spline with not-a-knot end conditions might be preferable to splrep.
	
	Chuck
	

	
	
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