Example code in Differential Pulse Code Modulation

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Jiro Katto
Jiro Katto 2021-10-18
编辑： Jiro Katto 2021-10-18
Output of an example code in Differential Pulse Code Modulation in https://www.mathworks.com/help/comm/ug/differential-pulse-code-modulation.html is different from local calculation.
t = [0:pi/50:2*pi];
x = sawtooth(3*t); % Original signal
initcodebook = [-1:.1:1]; % Initial guess at codebook
% Optimize parameters, using initial codebook and order 1.
[predictor,codebook,partition] = dpcmopt(x,1,initcodebook);
% Quantize x using DPCM.
encodedx = dpcmenco(x,codebook,partition,predictor);
% Try to recover x from the modulated signal.
decodedx = dpcmdeco(encodedx,codebook,predictor);
distor = sum((x-decodedx).^2)/length(x) % Mean square error
Example output on the wab page is 0.0063, but locally executed answer is 8.6801e-04. "codebook" seems strange in the last value (0.4791, that is smaller than the previous value 0.7008) as below. Is this a bug or something else ?
codebook =
-1.7571 -1.2431 -0.8946 -0.7118 -0.6000 -0.5000 -0.3999 -0.2987 -0.1945 -0.0867
0.0048 0.0981 0.1915 0.2963 0.3991 0.4998 0.5882 0.6283 0.6543 0.7008
0.4791

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