How can i find the derivative of a vector?

I have a vector 1x80. If i put x(1,80) and y (the values of the vector from 1 to 80), i have a plot. I do not know the function which describes the plot. I want to plot the derivatives of the unknown fuction.

Answer 1

[pfb]

You can do that approximately.

 % this is the "finite difference" derivative. Note it is  one element shorter than y and x
 yd = diff(y)./diff(x);

 % this is to assign yd an abscissa midway between two subsequent x
 xd = (x(2:end)+x(1:(end-1)))/2;

 % this should be a rough plot of your derivative
 plot(xd,yd)

Of course the reliability of the above procedure depends on the thickness of your grid x as well as on the properties of y.

You could perhaps do a slightly (cosmetically) better job by interpolating your data using interp1.

[Emmanouil Poulakis]

Thank you!I think this is helpful for me.When you say to interpolate my data, you mean to find a function which desribes the data?Is it easy to give me an example how to do this..