Add an element to a vector after taking difference

Dear Matlab community,

I am currently running some stationarity test, for which I take log-differences. However, if stationatiry tests still suggest non-stationarity, I would have to take the second difference.

The problem obviously is, that taking another difference changes the vector size, as now some of my variables are by 1 element shorter (those with the second difference).

I would like to add a zero as the first element to those column vectors, in order to restore equal dimensions.

It would basically look like this:

A =
X
X
X

B=
0
X
X
X

Thank you very much in advance!

Chris

Answer 1

[Star Strider]

That is easy enough to do:

B = [0; A];

However another way might be to use interp1 to artificially ‘stretch’ ‘A’:

A = randi(9, 14, 1);                            % Create Data: ‘A’
Ax = [1:14]';                                   % Independent Variable Vector For ‘A’
Bx = [1:15]';                                   % Independent Variable Vector For ‘B’
B = interp1(Ax, A, Bx, 'linear', 'extrap');     % Interpolate/Extrapolate To Calculate ‘B’

I offer it as an alternative.

[Christoph Meier]

Thank you very much, that does exactly what I was after!

[Star Strider]

My pleasure!