Question on using interpolate function

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Deepa Maheshvare
Deepa Maheshvare 2020-1-29
评论： Sindar 2020-1-29
This is a follow-up to my previous post here. I want to find the x value at which data has 5.0 (first occurence).
I tried using the find function suggested in the comments.
l = load('var.mat'); % file attached
l = l.unnamed;
x = l(:,1);
data = l(:,2);
tsinterp = getinterpmethod(x)
xmatch = x(find(data == 5.0,1))
The answer that I obtain is 1.71. However, the first occurrence of 5.0 is at 0.20 (x value). I'm not sure what's going wrong.
Any suggestions on how to proceed will be really helpful

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采纳的回答

Sindar
Sindar 2020-1-29
Check your data again. "data" is slightly less than 5 until x=0.485, and the first point exactly equal to 5 is x=1.71. You could add a tolerance like so:
tol = 1e-4;
xmatch = x(find(data >= 5.0-tol,1,'first'))
  2 个评论
Deepa Maheshvare
Deepa Maheshvare 2020-1-29
Hi, Many thanks for the response. Could you please explain why 1,'first') is required? I understand first picks the first occurrence. Could you please explain why 1 is required?
Sindar
Sindar 2020-1-29
"1" tells the number of occurences you want, in case there are multiple. 'first' is the direction; it isn't required, since it is the default, but I like to include it out of habit

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更多回答（1 个）

Walter Roberson
Walter Roberson 2020-1-29
See ismembertol()
The data that is stored corresponding to time 0.20, is not bit-for-bit identical to the representation for double precision 5.0. If you were to subtract 5 from the content at that location you would get something not exactly 0.

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