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Interpolating a double array

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Vaultec
Vaultec 2014-7-1
编辑： Youssef Khmou 2014-7-2
So far I am given a plot that is a 33x1 double. How do I interpolate the data so I can have a total of 1000 data sets?
I dont quite get how to use the interp1 or interp2 function in this case.
attached is the figure
In addition after I have got the derivative of the data, how do i find the zeroes on it? (figure14)

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Youssef Khmou
Youssef Khmou 2014-7-2
编辑：Youssef Khmou 2014-7-2
There is an alternative to interpolation functions :
% Given the vector r of 33x1 :
r=randn(33,1);
y=upsample(r,30);
% y is 990x1

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dpb
dpb 2014-7-1
编辑：dpb 2014-7-2
Presuming you have x,y in order to have generated the plots (if not, simply retrieve 'x|ydata' from the axes)
A)
xi=linspace(x(1),x(end),1000); % 1000 points between x range
yi=interp1(x,y,xi); % interpolate at those points
B)
xinflect=find(abs(sign(diff(y)),2)==2); % find points slope changes sign
NB: the above finds all points of maxima/minima, if need which keep the sign and select based on it. I'll leave which is which as "exercise for the student"... :)

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