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Asked: 2026-06-11T23:02:01+00:00

I am not getting the desired 2D linear interpolation functionality with LinearNDInterpolator. The following

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I am not getting the desired 2D linear interpolation functionality with LinearNDInterpolator. The following piece of code is trying to do an interpolation between the 4 knot points (0,0), (1,0), (0,1), (1,1). interp2d gives me the expected (linear-interpolated) result but LinearNDInterpolator is doing something else, which I am unable to figure out. Perhaps I am not using the API correctly. Unfortunately, I can’t find detailed docs on the usage. Can someone please help or point me to the right forum (mathoverflow ?) to write to ?

>>> f = interp2d([0,1,0,1], [0,0,1,1], [0,1,2,4])
>>> f(0.5,0.5)
array([ 1.75])
>>> g = LinearNDInterpolator([[0,0],[1,0],[0,1],[1,1]], [0,1,2,4])
>>> g(0.5,0.5)
array(2.0)
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1 Answer

  1. Editorial Team

    From http://docs.scipy.org/doc/scipy/reference/generated/scipy.interpolate.LinearNDInterpolator.html:

    The interpolant is constructed by triangulating the input data with Qhull [R15], and on each triangle performing linear barycentric interpolation.

    In your case, the triangles chosen appear to share the (0,0), (1,1) edge. Since (0.5, 0.5) is midway between (0,0) and (1,1), the interpolated value lies between the values at those vertices, so it is (0+4)/2 = 2.0.

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