createLags function - Hows does it compute ?

Question

Jan Morawietz 2014-11-25

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https://ww2.mathworks.cn/matlabcentral/answers/164297-createlags-function-hows-does-it-compute

回答： Jan Morawietz 2014-11-25

I'm currently trying to understand a matlab code of trend following. At some point, the code uses Matlab's "createLages" function. Can someone please explain me how this function works?

If I follow the official Matlab example, the function gives me:

x = [1 2 3 4; -1 -2 -3 -4]';
y = createLags(x, [-1 0 2]);
y =
       2    -2     1    -1   NaN   NaN
       3    -3     2    -2   NaN   NaN
       4    -4     3    -3     1    -1
     NaN   NaN     4    -4     2    -2

For explanation, "Matlab-file-help" example says:

"predictorMatrix (outcome) is a numObs-by-numDim*numLags matrix of the shifted versions of the input matrix"

However, if I follow this approach I'd get something like

t = [(x-1) (x-0) (x+2)]
   0    -2     1    -1     3     1
       1    -3     2    -2     4     0
       2    -4     3    -3     5    -1
       3    -5     4    -4     6    -2

... which of course I can't multiply with x anymore..

Any advice greatly appreciated!

Best