How to calculate the energy of details and approxmiations coefficients of discret wavelet transform ?

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afef 2017-7-20

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https://ww2.mathworks.cn/matlabcentral/answers/349624-how-to-calculate-the-energy-of-details-and-approxmiations-coefficients-of-discret-wavelet-transform

评论： Mohan Das 2022-12-8

Hi everyone, i calculate the energy of details and approxmiations coefficients of discret wavelet transform .i used DWT(Daub4) Here is the code

 for n=1:23
     deriv=(val(n,:))/2.559375;
    t=(0:length(deriv)-1)/Fs;
    result{n} = filtfilt(d1,deriv);
 [c,l]=wavedec(result{n},4,'db4');
    [cd1,cd2,cd3,cd4]=detcoef(c,l,[1,2,3,4]);
    cA4=appcoef(c,l,'db4',4);
    [Ea,Ed]=wenergy(c,l)
    energie{n} = {Ea, Ed};
  end

And when i was looking for the formula of the energy i found this :

and as i understand the energy is the percentage of energy corresponding to the approximation and the details

So when i was trying to write a C code using this formula and the values of cd1,cd2,cd3,cd4 i don't get the same values that i have with matlab So i want to know where i wrong ?

i mean to calcuate the energy i should use [cd1,cd2,cd3,cd4]??

Please i need a clarification,Thanks

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Sandeep Nayak 2019-11-8

yes. cd1,cd2,cd3,cd4 are the details coefficients and the command wenergy gives the percentage of energy not the actual energy. you can calculate the percentage energy by the expression i.e. percentage energy due to approximation = (energy of approximation-energy of details)/energy of approximation *100. similarly % energy due to details = 100-% energy due to approximation. energy of approximation is sum of square of approximation coefficients and energy of details is sum of square of details coefficients. Hope you got your answer..