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MathGroup Archive 2006

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Re: Interpolating data

  • To: mathgroup at smc.vnet.net
  • Subject: [mg64145] Re: Interpolating data
  • From: Bill Rowe <readnewsciv at earthlink.net>
  • Date: Thu, 2 Feb 2006 00:07:12 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

On 2/1/06 at 4:34 AM, nogarybko at yahoo.com (Noga) wrote:

>Hi, I'm trying to use the function "Interpolate" on a data of the
>kind:

>aaa = {{0,
>3, -4.7202`}, {0, 7, 17.5902`}, {-20, 0, -0.418`}, {-10, 0,
>17.3249`}, {0,
>0, -9.9187`}, {5, 0, -46.7828`}, {17.5`, 0, -51.2055`}, {-15, 5,
>-5.1367`}, { 7.5`, 5, 17.2389`}, {-17.5`, 10, -4.0567`}, {-5, 10,
>17.4435`},
>{0, 10,
>16.4173`}, {5, 10, 9.0035`}, {0, 12.5`, 9.4378`}, {0, 15,
>15.1786`}, {0, 17.5`, 15.3475`}, {0, -2, -54.6795`}, {20, 0, \
>17.5902`}, {10, 0, 17.3249`}, {-5, 0, -9.9187`}};

>I couldn't understant why it can't do it.

You haven't said what you tried, what you expected nor what response you got. So, my comments here are a *guess* as to what you are trying to do and what you may have done. If you tried

Interpolate[aaa]

I would expect Mathematica to return Interpolate[aaa] with aaa evaluated unless you have defined Interpolate. The built-in function is Interpolation.

However, with this data Interpolation won't work either because of the dimensions of the data array. You can get an interpolating function with ListIngerpolation, i.e.,

ListInterpolation[aaa,InterpolationOrder->{3,2}]

For this data, the InterpolationOrder->{3,2} is needed to avoid the warning message you will get without it. You need an array with at least 4 columns to use the default cubic interpolation.

BTW. although ListInterpolation will create a InterpolatingFunction it isn't clear this will be what you want. ListInterpolation assumes the data consists of z values with the x,y coordinates specified by the position of each value. If your data is intended to be {x,y,z} triplets and you want to get an interpolated z value for given {x,y} values, ListInterpolation won't do what you want.
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