On Jun 1, 2011, at 9:24 AM, Clement LAUZIN wrote:
Hello,
I have a x,y,z file.Z is not corresponding to a simple analytical
function of x and y (see below).
I am trying to find the minimum location of this surface and the z
value corresponding to this location by a spline interpolation or
from a polynomial fit.
I tried with the akima package but as the location of the point I am
looking for (the minimum) is outside of the convex hull it's not
giving any answer.
I do not think that is the reason akima::interp is failing. (For one
thing the minimum is not outside the convex hull of x and y.) Note
that the help page says that x and y cannot be collinear but yours
appear to be so.
> table(ZZ$x)
4.05 4.1 4.15 4.2 4.25 4.3 4.35
5 5 5 5 5 5 5
> table(ZZ$y)
60 67.5 75 82.5 90
7 7 7 7 7
I took a shot at jittering the x and y and reapplying interpp ... and
ended up with what appeared to be useless junk.
If you look at the data with contourplot you can see it would place
the minimum at around z=-175 at x=4.24, y=67. However, the contourplot
and associated help pages say there is no documentation for the
algorithm used.
contourplot(z ~ x + y, data=ZZ, at=seq(-140, -180 , by= -0.5),
interp=TRUE)
If someone has any idea or any suggestion?
Thank you in advance Pierre
x y z
4.1 60 -152.1719593
4.1 75 -171.136801
4.1 90 -170.4604774
4.2 60 -168.7745552
4.2 75 -174.9667333
4.2 90 -172.1853334
4.3 60 -173.7736418
4.3 75 -171.6712745
4.3 90 -167.6662458
4.05 60 -137.8379387
4.15 60 -162.2264066
4.25 60 -172.4453286
4.35 60 -173.2123715
4.05 67.5 -158.8239625
4.1 67.5 -167.314534
4.15 67.5 -172.586182
4.2 67.5 -175.2217594
4.25 67.5 -175.7162683
4.3 67.5 -174.4890566
4.35 67.5 -171.8940061
4.05 75 -165.4388778
4.15 75 -174.1460392
4.25 75 -174.022344
4.35 75 -168.2149168
4.05 82.5 -166.4026077
4.1 82.5 -170.9199652
4.15 82.5 -172.9923449
4.2 82.5 -173.0803255
4.25 82.5 -171.5739101
4.3 82.5 -168.8024715
4.35 82.5 -165.0431276
4.05 90 -166.2592978
4.15 90 -172.2861302
4.25 90 -170.5383652
4.35 90 -163.8389615
______________________________________________
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
David Winsemius, MD
West Hartford, CT
______________________________________________
R-help@r-project.org mailing list
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
