Re: InterpolatingPolynomial error message

• To: mathgroup at smc.vnet.net
• Subject: [mg115733] Re: InterpolatingPolynomial error message
• From: Barrie Stokes <Barrie.Stokes at newcastle.edu.au>
• Date: Wed, 19 Jan 2011 05:28:56 -0500 (EST)

```Hi Victor

1. The form of your data is not right for InterpolatingPolynomial (see the online documentation).

With

data2 = {{{105, 1.5}, 33.0127}, {{110, 1.5}, 32.2962}, {{115, 1.5},
31.6448}, {{120, 1.5}, 31.054}, {{125, 1.5},
30.5196}, {{130, 1.5}, 30.0374}, {{135, 1.5},
29.6036}, {{140, 1.5}, 29.2143}}

the command would then be

InterpolatingPolynomial[data2, {x, y}]

to get an interpolating surface in 3D. (I am assuming that is what " i am trying to get a function" means.)

This input however gives the message

InterpolatingPolynomial::poised: "The interpolation points {{105,1.5},{110,1.5},{115,1.5},{120,1.5},{125,1.5},{130,1.5},{135,1.5},{140,1.5}} are not poised, so an interpolating polynomial of total degree 3 could not be found"

If you then do

data3 = First /@ data2

to get the {x,y} coordinates, and then do

ListPlot[ data3 ]

You'll see what is retrospectively obvious, that your original 3D points project onto a straight line on the (x,y) plane. (That's what the "not poised" message means.) How do you imagine Mathematica could construct an interpolating *surface* from this data?

Cheers

Barrie

>>> On 18/01/2011 at 9:52 pm, in message <201101181052.FAA11815 at smc.vnet.net>,
VICTOR <victor.herasme at gmail.com> wrote:
> Hi,
>
> i am trying to get a function for this data set:
>
> data={{105,1.5,33.0127},{110,1.5,32.2962},{115,1.5,31.6448},{120,1.5,31.054}
> ,{125,1.5,30.5196},{130,1.5,30.0374},{135,1.5,29.6036},{140,1.5,29.2143},...}
>
> i execute the command:
>
> P=InterpolatingPolynomial[data,{x,y,z}]; And i get this error message:
>
> InterpolatingPolynomial::ipab: Abscissa specification 105 in
> {105,1.5,33.0127} is not a point in 3 dimensions. >>
>
> I dond't know what's going on. Can anyone help me please ? Regards,
>
> Victor

```

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