interpolate text file data onto different time axis

Question

Michael 2014-7-28

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回答： Michael 2014-7-28

Hello,

I have a text file which when imported creates a 226 x 2 matrix, with time being the (:,1) and SSH being (:,2). I want to compare and plot this data on some data I have created which is on a 723 x 1 axis. I have tried interp1 and I keep getting all NaN's apart from a few numbers here:

interp1(data(:,1), data(:,2), createddata) so like interp1(226x1, 226x1, 723x1)

I also tried making my own xaxis (1:723) and trying that but it didn't work...

Can someone help me?

thanks in advance! Michael

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Michael Haderlein 2014-7-28

Your createddata vector is 1:723? As all numbers in the first column (=x) are outside the interval 1:723, it's clear that you only get NaNs. You need to provide times at your createddata vector.

Michael 2014-7-28

I have just tried using the time values (given in a separate file) from 1993-2012 in a 723x1 matrix but I still get NaN's. Is this what you meant I should do? maybe I have misunderstood you.

t file = 723 x 1 (1.9930:1.206)

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Answer 1

dpb 2014-7-28

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As the other Michael says, "Houston, we have a problem!"

How do you want these data to line up with each other? How does the time relationship of the first point in the above data set relate to the first point in your series of length 723? Likewise for the last. If you're trying to stretch the 226 over 723 points just on a 1:1 basis between first and last, you don't need to use interp1, just set the time for the 226 points via

t1=linspace(1,723,226);

or, generically,

t1=linspace(1,length(series2),length(series1));

If there's some other way they're to correlate, need to define what that relationship is and if the time in these data is significant create a time vector between those two points similarly except use the time values instead of 1:N