# [SciPy-User] griddata interpolation methods

Gökhan Sever gokhansever@gmail....
Thu Apr 25 11:13:27 CDT 2013

```Hello,

I am using scipy.interpolate.griddata to interpolate a value from a table
of values. Below is the code, also attached in this e-mail:

# griddata interpolation method test
#
import itertools
import numpy as np
from scipy.interpolate import griddata
#
r_1_ry = np.array([   0.,   2.,   3.,   4.,   6.,   8.,  10.,  15.,  20.,
25.])
r_2_ry = np.array([  10.,  20.,  30.,  40.,  50.,  60.,  80., 100., 150.,
200., 300., 400., 500., 600.,1000.,1400.,1800.,2400.,3000.])
eff_ry = np.zeros((len(r_2_ry), len(r_1_ry)))
eff_ry[:,0] = [  .00,  .00,  .00,  .00,  .00,  .00,  .00,  .00,  .00,  .00,
.00,  .00,  .00,  .00,  .00,  .00,  .00,  .00,  .00]
eff_ry[:,1] = [  .02,  .00,  .00,  .00,  .00,  .00,  .00,  .00,  .02,  .04,
.10,  .10,  .10,  .17,  .15,  .11,  .08,  .04,  .02]
eff_ry[:,2] = [  .03,  .02,  .00,  .00,  .00,  .01,  .08,  .14,  .25,  .30,
.33,  .36,  .36,  .40,  .37,  .34,  .29,  .22,  .16]
eff_ry[:,3] = [  .04,  .03,  .02,  .02,  .03,  .13,  .23,  .32,  .43,  .46,
.51,  .51,  .52,  .54,  .52,  .49,  .45,  .39,  .33]
eff_ry[:,4] = [  .05,  .06,  .13,  .23,  .30,  .38,  .52,  .60,  .66,  .69,
.72,  .73,  .74,  .72,  .74,  .71,  .68,  .62,  .55]
eff_ry[:,5] = [  .05,  .12,  .28,  .40,  .40,  .57,  .68,  .73,  .78,  .81,
.82,  .83,  .83,  .83,  .82,  .83,  .80,  .75,  .71]
eff_ry[:,6] = [  .00,  .17,  .37,  .55,  .58,  .68,  .76,  .81,  .83,  .87,
.87,  .88,  .88,  .88,  .88,  .88,  .86,  .83,  .81]
eff_ry[:,7] = [  .00,  .17,  .54,  .70,  .73,  .80,  .86,  .90,  .92,  .93,
.93,  .93,  .93,  .94,  .94,  .94,  .96,  .92,  .90]
eff_ry[:,8] = [  .00,  .00,  .55,  .75,  .75,  .86,  .92,  .94,  .95,  .95,
.96,  .96,  .96,  .98,  .98,  .95,  .94,  .96,  .94]
eff_ry[:,9] = [  .00,  .00,  .47,  .75,  .79,  .91,  .95,  .96,  .96,  .96,
.97,  .97,  .97, 1.00, 1.00, 1.00, 1.00, 1.00, 1.00]
# Creating data point coordinates for use in griddata function
coords = list(itertools.product(*(r_2_ry, r_1_ry)))

interp1 = griddata(coords, eff_ry.flatten(), (50., 10.), method='linear')
interp2 = griddata(coords, eff_ry.flatten(), (50., 10.), method='nearest')
interp3 = griddata(coords, eff_ry.flatten(), (50., 10.), method='cubic')

print interp1
print interp2
print interp3

Running this code, I get the following results:

:!python Desktop/griddata_test.py
nan
0.58
nan

Why it produces nan for 'linear' and 'cubic' methods? I remember running
this code in an older scipy version with 'linear' switch and it was working
fine. Though, I can't remember the version of scipy that tested it before.
Was a there change in griddata since past?

Currently, I have:

np.__version__
'1.8.0.dev-82c0bb8'

scipy.__version__
'0.12.0.dev-2f17ff2'

--
Gökhan
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```