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hello i have an EEG signal form 14 channels.

i want to perform a diffusion map on each channel separately.

i have done STFT on the data.

The sample rate is 128H,

I took a window size of 256 and i have done 90% overlap. The size of the matrix is (129*766)

now i want to decompose the signal in 5 subbands:

- Delta (0–4 Hz)
- Theta (4–8 Hz)
- Alpha (8–16 Hz)
- Beta (16–32 Hz)
- Gamma (32–64 Hz)

for later on using diffusion maps on the data as 5 dimension matrix.

So after the decomposition i should have a (5*766) matrix, and one more vector for classification (1*766) There are events in [T=45s', 65s' , 90s' , 92s'] shown in the pic.

I wrote this code for the decomposition after some web search:

waveletFunction = 'db1';

[C,L] = wavedec(mySignal,5,waveletFunction);

%Calculation The Coificients Vectors of every Band :

cD1 = detcoef(C,L,1); %NOISY

cD2 = detcoef(C,L,2); %GAMMA

cD3 = detcoef(C,L,3); %BETA

cD4 = detcoef(C,L,4); %ALPHA

cD5 = detcoef(C,L,5); %THETA

cA5 = appcoef(C,L,waveletFunction,5); %DELTA

% Calculation the Details Vectors of every Band :

D1 = wrcoef('d',C,L,waveletFunction,1); %NOISY

Gamma = wrcoef('d',C,L,waveletFunction,2); %GAMMA

Beta = wrcoef('d',C,L,waveletFunction,3); %BETA

Alpha = wrcoef('d',C,L,waveletFunction,4); %ALPHA

Theta = wrcoef('d',C,L,waveletFunction,5); %THETA

Delta = wrcoef('a',C,L,waveletFunction,5); %DELTA

my questions are?

- how can i know if the code is correct and can i verify it ?
- when i use 'a' in the delta coefficient i get values *10^3 larger than the other coefficients , and when i use 'd' the values are in the same order.
- For my understanding the STFT(spectrogram plot) doesn't help my cause except maybe to distinguish the incidents in the time scale, am i right?
- What i need to do next for the diffusion map?
- how can i insert the classification vector?
- sadly i'm not sure what the meaning of the decomposition and how it can help me?

i hope someone can help me

best regards

yair

Mahsa Hassankashi
on 3 Aug 2021

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