Extrapolation of irregular sampled data

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Adili Wasi
Adili Wasi on 27 Jul 2019
Edited: John D'Errico on 4 Aug 2019
Hey I am very new to MatLab and I require urgent assistance.
I have a data set comprising of dates and observed level of phenomena, However the data was not sampled at a regular interval and I need to obtain the level of phenpmena past the sample data. How can I go about this?
Here is my data set
DTN WRL
__________ ___
7.093e+05 18
7.0955e+05 3
7.0964e+05 38
7.0958e+05 15
7.1615e+05 45
7.1785e+05 45
7.2662e+05 14
7.2723e+05 17
7.276e+05 18
7.2762e+05 16
7.2769e+05 18
7.2997e+05 16
  3 Comments
Walter Roberson
Walter Roberson on 28 Jul 2019
Is that numbers about dentatin versus WRL-68 ?
Walter Roberson
Walter Roberson on 4 Aug 2019
Must not have been urgent after all.

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Answers (1)

John D'Errico
John D'Errico on 28 Jul 2019
Edited: John D'Errico on 4 Aug 2019
Um, lets be serious. You want to extrapolate that mess?
plot(DTN,WRL,'o')
grid on
Seriously? Exactly what would you draw for that curve, if you were to draw it by hand? How far do you think you can intelligently extrapolate it?
I've fit it with a straight line model, which is about as much as the data is worth. Well, actually, the best model might arguably be a constant. You have effectively three data points. At the low end, the noise is so large as to be virtually random values, spanning the entire range of your data.
I'm sorry, but any extrapolation here would arguably be an egregious misuse of mathematics/statistics. Even extrapolating the straight line fit seems a bit random of an idea. When your data is highly noisy, then extrapolation is a virtually random thing. What you need to understand is that extrapolation is a dangerous thing. Done poorly, on bad, noisy data, you can arrive at any conclusion you wish to suggest.
Always look at your data. Does what you want to do make any sense in context of the data? The point of my response is that extrapolation is a really bad idea on this data. If you seriously want to do something like that, you need to get better data. Down at the low end for example, is there a reason why 4 samples, taken vitually at the same pioint, give 4 virtually random numbers as a result? You need to spend some time and understand the process. how should it behave? What shape would you expect? Don't just take any set of data and assume it can be arbitrarily extrapolated.
My favorite quote about mathematics and extrpolation comes from Mark Twain, in "Life on the MIssissippi".
“In the space of one hundred and seventy six years the Lower Mississippi has shortened itself two hundred and forty-two miles. That is an average of a trifle over a mile and a third per year. Therefore, any calm person, who is not blind or idiotic, can see that in the Old Oölitic Silurian Period, just a million years ago next November, the Lower Mississippi was upwards of one million three hundred thousand miles long, and stuck out over the Gulf of Mexico like a fishing-pole. And by the same token any person can see that seven hundred and forty-two years from now the Lower Mississippi will be only a mile and three-quarters long, and Cairo [Illinois] and New Orleans will have joined their streets together and be plodding comfortably along under a single mayor and a mutual board of aldermen. There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact.”

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