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MathGroup Archive 2007

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Re: 2D interpolation

  • To: mathgroup at smc.vnet.net
  • Subject: [mg72916] Re: [mg72901] 2D interpolation
  • From: "Josef Otta" <josef.otta at gmail.com>
  • Date: Thu, 25 Jan 2007 06:39:24 -0500 (EST)

Hi Fabrice,
if you use Interpolation your sampling points should lie on regular grid.
That is one of possible reasons why it does not not work. In general case
you can use for example Delaunay triangulation and resample your original
data(included in DiscreteMath`ComputationalGeometry`.) There is nothing
wrong with real numbers, but problem is in choosing sampling points.

Regards,
Josef Otta
http://home.zcu.cz/~jotta


2007/1/24, Jouvenot, Fabrice <F.Jouvenot at liverpool.ac.uk>:
>
> Hello,
>
> I am asking (again) for your knowledge to help me.
> I try to have a 2 dimensional interpolation of points {x, y, f(x,y)}.
> After some try, I wrote these lines (as an exemple of what I want to do)
> that works :
> ________________________________________
>
> data = {{1, 1, -10}, {1, 2, 2}, {1, 3, 3}, {1, 4, 4}, {1, 5, 5}, {2, 1,
> 2}, {2, 2, 4}, {2, 3, 6}, {2, 4, 8}, {2, 5, 10}, {3., 1, -9}, {3, 2, 6},
> {3, 3, 90}, {3, 4, 12}, {3, 5, 15}, {4, 1, 4}, {4, 2, 8}, {4, 3, 12},
> {4, 4, 16}, {4, 5, 20}, {5, 1, 5}, {5, 2, 10}, {5, 3, 15}, {5, 4, 20},
> {5, 5, 40.5}};
>
> MatrixForm[data]
>
> test[x_, y_] := Interpolation[data][x, y];
>
> test[1.5, 1.5]
>
> Plot[test[x, 1], {x, 1, 5}];
>
> Plot[test[x, x], {x, 1, 5}];
>
> Plot3D[test[x, y], {x, 1, 5}, {y, 1, 5}];
>
> ________________________________________
>
>
> The problem is that when I want to use a point with a real x or y like
> {1.23, 1.1, -10}, nothing works anymore.
> I think that I miss something essential and fundamental, but I don'y
> know why...
> Thanks for your help,
> Cheers,
>
> Fabrice.
>
>


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