What makes the difference between griddata and griddatan?

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Peng Liu 2017-2-2

1
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https://ww2.mathworks.cn/matlabcentral/answers/323117-what-makes-the-difference-between-griddata-and-griddatan

评论： Honglei Chen 2017-2-3

Since griddatan is the n-d generalization of griddata, I assume that for 2-d scenarios, they should have identical behavior. This is true for most cases. For example:

uv = [-6,-13;-3,-9;-9,-2;-12,7;25,-14;16,-24;3,15];
xy = [8,6;15,1;4,-11;-3,9];
z1 = griddata(uv(:,1),uv(:,2),uv(:,2),xy(:,1),xy(:,2))
z2 = griddatan(uv,uv(:,2),xy)

The output is:

z1 =
  6.0000
     NaN
-11.0000
  9.0000
z2 =
  6.0000
     NaN
-11.0000
  9.0000

But in the following example, griddata gives valid output while griddatan fails.

uv = [0,0;0,2;2,2;2,0];
xy = [1,1;3,1];
z1 = griddata(uv(:,1),uv(:,2),uv(:,2),xy(:,1),xy(:,2))
z2 = griddatan(uv,uv(:,2),xy)

The error message indicates that some internal check of the convex hull in griddatan fails. But why is that? Why griddata run without a similar convex check? Thanks.