[SciPy-user] Cookbook: Interpolation of an N-D curve error

[Angus McMorland]

Fernando Perez wrote:
>> ipdb> whatis s
>> <type 'float'>
>> ipdb> s
>> WARNING: Failure executing file: <spl.py>
>>
>> In [23]:
>>
>> Requesting s kicks me out of the debugger altogether.
> 
> Not an answer to your question, but 's' is a pdb command:

Doh, of course! Thanks for that. Following on with the actual problem:

ipdb> print s
3.0

So no problems there in fact. Just while I was there I tried:

ipdb> print u
[ 0.  0.  0.  0.  0.  0.  0.  0.  0.  0.  0.  0.  0.  0.  0.  0.  0.  0.
  0.  0.  0.  0.  0.  0.  0.  0.  0.  0.  0.  0.  0.  0.  0.  0.  0.  0.
  0.  0.  0.  0.  0.  0.  0.  0.  0.  0.  0.  0.  0.  0.  0.  0.  0.  0.
  0.  0.  0.  0.  0.  0.  0.  0.  0.  0.  0.  0.  0.  0.  0.  0.  0.  0.
  0.  0.  0.  0.  0.  0.  0.  0.  0.  0.  0.  0.  0.  0.  0.  0.  0.  0.
  0.  0.  0.  0.  0.  0.  0.  0.  0.  0.]
ipdb> u.shape
/home/amcmorl/tmp/spl.py
     21 # find the knot points
---> 22 tckp,u = splprep([x,y,z],s=s,k=k,nest=-1)
     23

ipdb> print w
[ 1.  1.  1.  1.  1.  1.  1.  1.  1.  1.  1.  1.  1.  1.  1.  1.  1.  1.
  1.  1.  1.  1.  1.  1.  1.  1.  1.  1.  1.  1.  1.  1.  1.  1.  1.  1.
  1.  1.  1.  1.  1.  1.  1.  1.  1.  1.  1.  1.  1.  1.  1.  1.  1.  1.
  1.  1.  1.  1.  1.  1.  1.  1.  1.  1.  1.  1.  1.  1.  1.  1.  1.  1.
  1.  1.  1.  1.  1.  1.  1.  1.  1.  1.  1.  1.  1.  1.  1.  1.  1.  1.
  1.  1.  1.  1.  1.  1.  1.  1.  1.  1.]
ipdb> w.shape
/home/amcmorl/tmp/spl.py
     20
     21 # find the knot points
---> 22 tckp,u = splprep([x,y,z],s=s,k=k,nest=-1)
     23
     24 # evaluate spline, including interpolated points

/usr/lib/python2.3/site-packages/scipy/interpolate/fitpack.py in splprep()
    215     iwrk=_parcur_cache['iwrk']
    216
t,c,o=_fitpack._parcur(ravel(transpose(x)),w,u,ub,ue,k,task,ipar,s,t,
--> 217                              nest,wrk,iwrk,per)
    218     _parcur_cache['u']=o['u']
    219     _parcur_cache['ub']=o['ub']

I.E. I can see the values, but not get the shape returned. My
understanding is that u should be the incrementing parameter for the
spline (and checking on the i686 (where the routine works):

In [11]:u
Out[11]:
array([ 0.        ,  0.00660902,  0.0123891 ,  0.02341715,  0.03388626,
        0.05189959,  0.068629  ,  0.08002793,  0.08344803,  0.09142408,
        0.09939328,  0.10562672,  0.10838236,  0.11531264,  0.12881276,
        0.13391073,  0.14557512,  0.1514497 ,  0.16502928,  0.17323899,
        0.18147124,  0.19263442,  0.20709241,  0.20862571,  0.21886334,
        0.22479777,  0.23564814,  0.2451128 ,  0.25976362,  0.26892058,
        0.27990341,  0.28739167,  0.29471638,  0.3012055 ,  0.31482816,
        0.32418042,  0.34062476,  0.34403043,  0.35805071,  0.36502075,
        0.37829313,  0.38401472,  0.3915394 ,  0.39294913,  0.4043306 ,
        0.4156923 ,  0.42120011,  0.43522407,  0.44540497,  0.46210282,
        0.47038053,  0.47715903,  0.49183298,  0.50998032,  0.51845474,
        0.53809475,  0.5530424 ,  0.56392821,  0.56784815,  0.57119358,
        0.57531501,  0.58558322,  0.59262561,  0.60861044,  0.62329971,
        0.63037712,  0.64413892,  0.65586238,  0.66734774,  0.68279714,
        0.69122243,  0.70602072,  0.71882921,  0.72595286,  0.7387055 ,
        0.74737882,  0.75263852,  0.76107314,  0.7737371 ,  0.78308686,
        0.78913781,  0.80321246,  0.81822862,  0.8354007 ,  0.84295247,
        0.84967894,  0.86107013,  0.87619586,  0.88717895,  0.89178471,
        0.89884305,  0.90861747,  0.91663593,  0.92117768,  0.93464362,
        0.95465968,  0.96749238,  0.97699623,  0.9824898 ,  1.        ])

So, it looks like the definition of u might be the problem. I see that
it looks like u is correctly defined as a float (from the "0."s,
although ipdb> u.dtype raises the same error as u.shape.

A.
-- 
Angus McMorland
email a.mcmorland at auckland.ac.nz
mobile +64-21-155-4906

PhD Student, Neurophysiology / Multiphoton & Confocal Imaging
Physiology, University of Auckland
phone +64-9-3737-599 x89707

Armourer, Auckland University Fencing
Secretary, Fencing North Inc.