how dwt and wavedec are different ? here why cA1 and C have diffrent values?

Question

amit_neuro 2013-3-9

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/66499-how-dwt-and-wavedec-are-different-here-why-ca1-and-c-have-diffrent-values

评论： Raul Souza Muniz 2021-7-5

采纳的回答： Wayne King

data=xlsread('E:\color\neha.xlsx');

data= data';

value1=data(1,:);

chan1= value1-mean(value1);

[cA1,cD1] = dwt(chan1,'db4');

[cA2,cD2] = dwt(cA1,'db4');

[cA3,cD3] = dwt(cA2,'db4');

[cA4,cD4] = dwt(cA3,'db4');

[cA5,cD5] = dwt(cA4,'db4');

[cA6,cD6] = dwt(cA5,'db4');

[cA7,cD7] = dwt(cA6,'db4');

[cA8,cD8] = dwt(cA7,'db4');

[cA9,cD9] = dwt(cA8,'db4');

[cA10,cD10] = dwt(cA9,'db4');

[C,L] = wavedec(chan1,10,'db4');

1 个评论
显示 -1更早的评论隐藏 -1更早的评论

Raul Souza Muniz 2021-7-5

Can I ask you something ? Do I have to do this manually. I mean, could I make an matrix and put all the c values and D values in the matrix with a for loop ? I cannot see a way to do this, because there is a long time since I programed in matlab. Really sorry for my dumb question.

Thank you very much

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Wayne King 2013-3-9

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/66499-how-dwt-and-wavedec-are-different-here-why-ca1-and-c-have-diffrent-values#answer_77994

编辑：Wayne King 2013-3-9

在 MATLAB Online 中打开

As you see, dwt() gives only a level 1 DWT, while wavedec gives you multiple levels. But you are correct that wavedec() simply iterates on the approximation coefficients of the previous level as expected.

Why do you say they are different? I do not see it. The first L(1) elements of wavedec should equal cA10 above

chan1 = randn(1024,1);
[cA1,cD1] = dwt(chan1,'db4');
[cA2,cD2] = dwt(cA1,'db4');
[cA3,cD3] = dwt(cA2,'db4');
[cA4,cD4] = dwt(cA3,'db4');
[cA5,cD5] = dwt(cA4,'db4');
[cA6,cD6] = dwt(cA5,'db4');
[cA7,cD7] = dwt(cA6,'db4');
[cA8,cD8] = dwt(cA7,'db4');
[cA9,cD9] = dwt(cA8,'db4');
[cA10,cD10] = dwt(cA9,'db4');
[C,L] = wavedec(chan1,10,'db4');

Now compare:

C(1:L(1))

with

cA10

Likewise, compare

C(L(1)+1:L(1)+L(2))

with

cD10

2 个评论
显示无隐藏无

amit_neuro 2013-3-9

编辑：amit_neuro 2013-3-9

thanks King. i got it.

But tell me on more thing, "is it necessary to reconstruct the cA10 to get the real signal?"

Wayne King 2013-3-9

It's only necessary if you have gone down to that level in the multiresolution analysis, if you go down to level 10, then you need the the final level approximation coefficients to achieve perfect reconstruction.

请先登录，再进行评论。

Answer 2

TONY SINGLA 2013-8-17

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/66499-how-dwt-and-wavedec-are-different-here-why-ca1-and-c-have-diffrent-values#answer_94494

hello

i have a doubt that how DWT calculates the values for the cd1,ca1 and cd2,ca2 and so on............... which *|formula |*it uses to calculate the values for the respective C and L values in case of 1D-DWT at multilevel

reply please waiting for your reply