Add an element to a vector after taking difference

Question

Christoph Meier 2015-9-3

0
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https://ww2.mathworks.cn/matlabcentral/answers/239320-add-an-element-to-a-vector-after-taking-difference

评论： Star Strider 2015-9-3

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

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Answer 1

Star Strider 2015-9-3

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https://ww2.mathworks.cn/matlabcentral/answers/239320-add-an-element-to-a-vector-after-taking-difference#answer_191172

在 MATLAB Online 中打开

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.