Alternative function to Matlab’s scatteredInterpolant for Python and C++ with given example

  c++, matlab, python

I was wondering if anyone would know how to translate a function I have from Matlab to Python and C++. The main problem I have is to find an interpolation function equivalent to Matlab’s scatteredInterpolant. I have searched for more information and found this other entry but I have not been able to adapt the code, so I was wondering if anyone would know.

The simplified Matlab function would be as follows

function data_out = test_interp (data_input)
U = rand(20,20);
V = rand(20,20);
[X,Y] = meshgrid(1:20,1:20);
% Create matrix with specific format.
aux_array = [reshape(U,[],1) reshape(V,[],1) reshape(X,[],1) reshape(Y,[],1)];
% Apply scatteredInterpolant with vector arrays.
FX = scatteredInterpolant(aux_array(:,1),aux_array(:,2), aux_array(:,3));
FY = scatteredInterpolant(aux_array(:,1),aux_array(:,2), aux_array(:,4));
% Apply FX and FY to the desired input.
data_out(:,1) = FX(data_input(:,1),data_input(:,2));
data_out(:,2) = FY(data_input(:,1),data_input(:,2));
end

What it would do would be to perform the interpolation between two matrices and apply them to some input data, a way to call the function would be: data_out = test_interp (rand(10,2))

I note the fact that the matrices are actually much larger and are not randomly generated, but they are useful to understand the effect.

I was testing and in Python what I managed to do is the following:

import numpy as np
from scipy.interpolate import griddata

def test_interp (data_input):
    # Generate 
    U = np.random.random([20, 20])
    V = np.random.random([20, 20])
    [X, Y] = np.meshgrid(np.linspace(1, 20, 20), np.linspace(1, 20, 20))
    xx = griddata((X.flatten(), Y.flatten()),U.flatten(),(data_input[:,0],data_input[:,1]),method='linear')
    yy = griddata((X.flatten(), Y.flatten()),V.flatten(),(data_input[:,0],data_input[:,1]),method='linear')
    data_mm = [xx, yy]
    return data_mm

But from what I was seeing the griddata function is not well implemented, I also tried with np.interp2d but I didn’t get the same thing.

With C++ the same thing happens to me, I wouldn’t know which function I should use to replace the Matlab function.

Source: Windows Questions C++

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