# Spline function

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## Spline function

 Hello everyone. I'm new to R and I'm using spline functions. With the command splinefun (x, y) I get the function of interpolating the values x and y. Later, I can evaluate that function for values of x by obtaining the respective values of y. The point is that I need the inverse operation, with the function, for a value of Y I need to know the value of x. Could you please help me? A cordial greeting         [[alternative HTML version deleted]] ______________________________________________ [hidden email] mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-helpPLEASE do read the posting guide http://www.R-project.org/posting-guide.htmland provide commented, minimal, self-contained, reproducible code.
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## Re: Spline function

 If I understand correctly, not in general possible. Suppose for a bunch of different x's the y's are all constant =0. What x would correspond to y = 1. Or suppose (x,y) pairs trace a sine function over several periods. Then there is no unique x corresponding to y = .5, say. Perhaps if you more explicitly specified the nature of your problem (e.g. is y monotonic in x?) some assistance might be provided. Cheers, Bert Bert Gunter "The trouble with having an open mind is that people keep coming along and sticking things into it." -- Opus (aka Berkeley Breathed in his "Bloom County" comic strip ) On Tue, Aug 14, 2018 at 8:48 AM, Tania Morgado Garcia <[hidden email]> wrote: >  Hello everyone. I'm new to R and I'm using spline functions. With the > command splinefun (x, y) I get the function of interpolating the values x > and y. Later, I can evaluate that function for values of x by obtaining the > respective values of y. The point is that I need the inverse operation, > with the function, for a value of Y I need to know the value of x. Could > you please help me? > A cordial greeting > >         [[alternative HTML version deleted]] > > ______________________________________________ > [hidden email] mailing list -- To UNSUBSCRIBE and more, see > https://stat.ethz.ch/mailman/listinfo/r-help> PLEASE do read the posting guide http://www.R-project.org/> posting-guide.html > and provide commented, minimal, self-contained, reproducible code. >         [[alternative HTML version deleted]] ______________________________________________ [hidden email] mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-helpPLEASE do read the posting guide http://www.R-project.org/posting-guide.htmland provide commented, minimal, self-contained, reproducible code.
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## Re: Spline function

 In reply to this post by ttmm The uniroot function can be used to find a value in a specified interval, if it exists. On Tue, Aug 14, 2018 at 3:30 PM Tania Morgado Garcia <[hidden email]> wrote: > >  Hello everyone. I'm new to R and I'm using spline functions. With the > command splinefun (x, y) I get the function of interpolating the values x > and y. Later, I can evaluate that function for values of x by obtaining the > respective values of y. The point is that I need the inverse operation, > with the function, for a value of Y I need to know the value of x. Could > you please help me? > A cordial greeting > >         [[alternative HTML version deleted]] > > ______________________________________________ > [hidden email] mailing list -- To UNSUBSCRIBE and more, see > https://stat.ethz.ch/mailman/listinfo/r-help> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html> and provide commented, minimal, self-contained, reproducible code. -- Gregory (Greg) L. Snow Ph.D. [hidden email] ______________________________________________ [hidden email] mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-helpPLEASE do read the posting guide http://www.R-project.org/posting-guide.htmland provide commented, minimal, self-contained, reproducible code.