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interp1 measurements drifting

Asked by Nikolaos Zafirakis on 24 Jul 2019
Latest activity Answered by Bhargavi Maganuru on 22 Aug 2019 at 10:47
I have some original data plotted below and I need to interpolate it with my other set of measurements. However whenever I run my interpolation function the initial measurements start at an unreal value. Both sets of data are different lengths.
Original Data
(y is Data, x is just number of measurements)
SS = (:,1:5)
SS1 = SS(:,4) % Time reference
SS2 = SS(:,1) % Data
K = interp1( SS1(1:end,1) , SS2(1:end,1) , RefernceTime(1:end,1),'pchip');
Interpolated data
(y is interpolated data and x is the reference times)

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dpb
on 24 Jul 2019
SS = (:,1:5)
is invalid syntax...A variable is missing on RHS, maybe???
SS1 = SS(:,4) % Time reference
SS2 = SS(:,1) % Data
K = interp1( SS1(1:end,1) , SS1(1:end,1) , RefernceTime(1:end,1),'pchip');
Looks like another typo in you've repeated the time() column as both the X and Y values for interp1 arguments.
K = interp1(SS(:,4),SS(:,2), RefernceTime,'pchip');
is probably closer to what you're intending.
Hello dpb thanks for spotting that, but this is a dummy copie of my code in the original my code is identical to what you suggested. I am still getting the error and our clueless in how to solve it.
So, SS1 is an array say about 32 columns.
SS2 is an array of equivalent columns.
referancetime is an array of 9 columns.
For some reason I get that massive increase at the beginning.
Can you attach SS and RefernceTime data files

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1 Answer

Answer by Bhargavi Maganuru on 22 Aug 2019 at 10:47

As you mentioned SS1 and SS2 are arrays of 32 columns, but in the line
K = interp1(SS1(1: end,1), SS2(1: end,1), RefernceTime (1: end,1),'pchip');
it is taking only one column of SS1 and SS2. You can directly use SS1, SS2 and ReferenceTime.
K = interp1(SS1, SS2, RefernceTime, 'pchip');
You can look at following code to interpolate array with 32 columns:
%random data
ss2=rand (1,32);
ss1= (1:32)
ReferenceTime=ss1
k=interp1(ss1, ss2, ReferenceTime, 'pchip')
plot (ss1, ss2,'o', ReferenceTime, k, ':.');
Refer to the following link for more information about “interp1” function:

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