I am a little confused by the documentation for scipy.interpolate.RegularGridInterpolator.
Say for instance I have a function f: R^3 => R which is sampled on the vertices of the unit cube. I would like to interpolate so as to find values inside the cube.
import numpy as np
# Grid points / sample locations
X = np.array([[0,0,0], [0,0,1], [0,1,0], [0,1,1], [1,0,0], [1,0,1], [1,1,0], [1,1,1.]])
# Function values at the grid points
F = np.random.rand(8)
Now, RegularGridInterpolator
takes a points
argument, and a values
argument.
points : tuple of ndarray of float, with shapes (m1, ), ..., (mn, ) The points defining the regular grid in n dimensions.
values : array_like, shape (m1, ..., mn, ...) The data on the regular grid in n dimensions.
I interpret this as being able to call as such:
import scipy.interpolate as irp
rgi = irp.RegularGridInterpolator(X, F)
However, when I do so, I get the following error:
ValueError: There are 8 point arrays, but values has 1 dimensions
What am I misinterpreting in the docs?
Ok I feel silly when I answer my own question, but I found my mistake with help from the documentation of the original regulargrid
lib:
https://github.com/JohannesBuchner/regulargrid
points
should be a list of arrays that specifies how the points are spaced along each axis.
For example, to take the unit cube as above, I should set:
pts = ( np.array([0,1.]), )*3
or if I had data which was sampled at higher resolution along the last axis, I might set:
pts = ( np.array([0,1.]), np.array([0,1.]), np.array([0,0.5,1.]) )
Finally, values
has to be of shape corresponding to the grid laid out implicitly by points
. For example,
val_size = map(lambda q: q.shape[0], pts)
vals = np.zeros( val_size )
# make an arbitrary function to test:
func = lambda pt: (pt**2).sum()
# collect func's values at grid pts
for i in range(pts[0].shape[0]):
for j in range(pts[1].shape[0]):
for k in range(pts[2].shape[0]):
vals[i,j,k] = func(np.array([pts[0][i], pts[1][j], pts[2][k]]))
So finally,
rgi = irp.RegularGridInterpolator(points=pts, values=vals)
runs and performs as desired.