differencing a time series

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Chithralekha 2013-8-10

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https://ww2.mathworks.cn/matlabcentral/answers/84469-differencing-a-time-series

I want to difference a time series till it becomes stationary.how to code it using matlab.i am writing my code below.please help me to continue it acf=autocorr of time series

l(k)=lower limit
u(k)=upper limit

if ((acf(k+1)<l(k)) || (acf(k+1)>u(k))),a time series is non-stationary.now i have to difference a time series till it becomes stationary.how to write using a single expression.

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dpb 2013-8-10

编辑：dpb 2013-8-10

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What's k supposed to represent--the k-th lag of the acf series or the acf after the k-th difference of x?

Maybe my utility function can help some w/ the complexity -- it's just syntactic sugar but by putting the logic expressions at a lower level it can often lead to seeing how to reduce expressions...

while ~all(iswithin(acf,l,u))
  ... do another difference here
end

where acf is presumed to be the acf at the kth iteration

iswithin is

function flg=iswithin(x,lo,hi)
% returns T for values within range of input
% SYNTAX:
%  [log] = iswithin(x,lo,hi)
%      returns T for x between lo and hi values, inclusive
flg= (x>=lo) & (x<=hi);