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matlabwhile-loopdo-whileentropy

Matlab : Plot of entropy vs digitized code length

[Tent Map][1] is a dynamical system that is discrete in time. Iterations of the map yields a time series.

The entropy of this system when discretized in 0/1 using a threshold = 0.5 is, H = log_2(2) = 0.69 approx. I want to obtain a graph with Y Axis as the entropy and X Axis as the Number of samples or the length of the time series. I have written a code for obatining the entropy by varying the length of the time series. The objective is to see at what length of the discretized time series, I get the entropy H. The code however, loops infinitely and never reaches the entropy value H. Can somebody please help in obtaining the graph? Thank you.

  [1]: https://en.wikipedia.org/wiki/Tent_map
Solution

  • You are saying that lambda must be EXACTLY equal to log(2). When the entropy drops below log(2) it skips over this value (for instance instead of exactly log(2) maybe an iteration is 0.69309 which is less). Try replacing the line

    while(lambda ~=H)

    with

    tol=0.01;
while(~(abs(lambda-H)<tol))

    this will mean that it quits whenever lambda is close to H (with in the tolerance tol).

    If your tol is too small (try 0.001) an iteration would jump over it again and you would be back to the problem you had before.