Interpolating a double array

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)

Answer 1

[Youssef Khmou]

There is an alternative to interpolation functions :

 % Given the vector r of 33x1 :
 r=randn(33,1);
 y=upsample(r,30);
 % y is 990x1

Answer 2

[dpb]

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"... :)