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Re: Reverse interpolation? [message #21207 is a reply to message #21201]

Thu, 17 August 2000 00:00

Martin Schultz
Messages: 515
Registered: August 1997

Senior Member

Craig Markwardt wrote:
>
> Martin Schultz <martin.schultz@dkrz.de> writes:
>
> Craig wrote:
>
>>
> ...
>> newxx = Spline( oldy, oldx, newy, 5. )
> ...
>
> If you are trying to match a lot of values, then I agree that the
> spline interpolation is one of the best solutions. However, I have
> had bad experiences with the SPLINE function. It tends to have
> problems when the points are too far apart, and it's also pretty slow.
> I found the Numerical Recipes version of spline interpolation to be
> much better (built in functions SPL_INTERP and SPL_INIT).
>
> If v1 is vector of values sampled at original altitudes a1, and you
> want to resample at new altitudes a2, then you do something like this:
>
> v2 = spl_interp(a1, v1, spl_init(a1, v1), a2)
>
> Now v2 has the newly sampled values. In principle a2 can be one value
> so even if you want a single value the spline interpolation can be
> useful, and even pretty fast.
>

I had looked into SPL_INTERP and SPL_INIT, but I found the
problem was that it does not allow for "smoothing" (more
correctly: controlling "the amount of tension that is applied to
the curve"). I certainly like the idea of controllin the
endpoints (which you can do only in SPL_INTERP). Are you aware of
a solution that can do both?

Martin

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[[
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[Message index]

		Re: Reverse interpolation? By: Craig Markwardt on Thu, 17 August 2000 00:00
		Re: Reverse interpolation? By: Martin Schultz on Thu, 17 August 2000 00:00
		Re: Reverse interpolation? By: Craig Markwardt on Wed, 16 August 2000 00:00
		Re: Reverse interpolation? By: promashkin on Wed, 16 August 2000 00:00
		Re: Reverse interpolation? By: Simon de Vet on Wed, 16 August 2000 00:00
		Re: Reverse interpolation? By: Martin Schultz on Wed, 16 August 2000 00:00

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