       Bug in Interpolation for multi-d data?

• To: mathgroup at smc.vnet.net
• Subject: [mg85979] Bug in Interpolation for multi-d data?
• From: oshaughn <oshaughn at northwestern.edu>
• Date: Fri, 29 Feb 2008 06:24:30 -0500 (EST)

```Hello,

Interpolation on multi-d data gives different answers depending on the
order in which the elements are *ordered* in the list.   As far as I
can tell, this is not documented.
The sorted element order seems to produce the right results.

Example 1:
dat = Flatten[
Table[{{x, y}, Sin[x] Sin[2 y]}, {x, -3, 3, 0.1}, {y, -3, 3, 0.1}],
1];
dat[[{1, 2, 3}]]
intp = Interpolation[dat];
ListPlot3D[Flatten /@ dat]
Plot3D[intp[x, y], {x, -3, 3}, {y, -3, 3}]

Example 2:
dat = Flatten[
Table[{{x, y}, Sin[x] Sin[2 y]}, {y, -3, 3, 0.1}, {x, -3, 3, 0.1}],
1];
dat[[{1, 2, 3}]]
intp = Interpolation[dat];
ListPlot3D[Flatten /@ dat]
Plot3D[intp[x, y], {x, -3, 3}, {y, -3, 3}]

Example 3:
dat = Flatten[
Table[{{x, y}, Sin[x] Sin[2 y]}, {y, -3, 3, 0.1}, {x, -3, 3, 0.1}],
1]//Sort;
dat[[{1, 2, 3}]]
intp = Interpolation[dat];
ListPlot3D[Flatten /@ dat]
Plot3D[intp[x, y], {x, -3, 3}, {y, -3, 3}]

Am I missing something obvious in the documentation?

```

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