wrcoef

Reconstruct single branch from 1-D wavelet coefficients

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    Syntax

    x = wrcoef(type,c,l,wname)
    x = wrcoef(type,c,l,LoR,HiR)
    x = wrcoef(___,n)

    Description

    x = wrcoef(type,c,l,wname) reconstructs the coefficients vector of type type based on the wavelet decomposition structure [c,l] of a 1-D signal (see wavedec for more information) using the wavelet specified by wname. The coefficients at the maximum decomposition level are reconstructed. The length of x is equal to the length of the original 1-D signal.

    x = wrcoef(type,c,l,LoR,HiR) uses the reconstruction filters LoR and HiR.

    x = wrcoef(___,n) reconstructs the coefficients at level n using any of the previous syntaxes.

    example

    Examples

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    Open Live Script

    Load a 1-D signal.

    load sumsin
s = sumsin;

    Perform a level 5 wavelet decomposition of the signal using the sym4 wavelet.

    [c,l] = wavedec(s,5,'sym4');

    Reconstruct the approximation coefficients at level 5 from the wavelet decomposition structure [c,l].

    a5 = wrcoef('a',c,l,'sym4');

    Reconstruct the detail coefficients at level 2.

    d2 = wrcoef('d',c,l,'sym4',2);

    Plot the original signal and reconstructed coefficients.

    subplot(3,1,1)
plot(s)
title('Original Signal')
subplot(3,1,2)
plot(a5)
title('Reconstructed Approximation At Level 5')
subplot(3,1,3)
plot(d2)
title('Reconstructed Details At Level 2')

    Figure contains 3 axes objects. Axes object 1 with title Original Signal contains an object of type line. Axes object 2 with title Reconstructed Approximation At Level 5 contains an object of type line. Axes object 3 with title Reconstructed Details At Level 2 contains an object of type line.

    Open Live Script

    This example shows how, starting with a multilevel 1-D discrete wavelet decomposition of a signal, you can obtain projections of the signal onto wavelet subspaces at successive scales and a scaling subspace. These projections are at the same time scale as the original signal. In other words, you can obtain a multiresolution analysis (MRA) based on the decimated discrete wavelet transform (DWT). You can recover the signal by summing the projections. For more information, see Practical Introduction to Multiresolution Analysis.

    Load and plot a signal.

    load noissin
plot(noissin)
title("Original Signal")

    Figure contains an axes object. The axes object with title Original Signal contains an object of type line.

    Use the wavedec function to obtain the discrete wavelet decomposition of the signal down to level 3 using the db4 wavelet. 

    level = 3;
wv = "db4";
[C,L] = wavedec(noissin,level,wv);

    Preallocate a matrix to save the MRA. The number of rows is one more than the level of decomposition, and the number of columns equals the length of the signal.

    mra = zeros(level+1,numel(noissin));

    Use the wrcoef function to obtain the projections of the signal onto the three wavelet (detail) subspaces. Then obtain the projection onto the final scaling (coarse or approximation) subspace. 

    for k=1:level
    mra(k,:) = wrcoef("d",C,L,wv,k);
end
mra(end,:) = wrcoef("a",C,L,wv,level);

    Confirm the sum along the rows of the MRA equals the original signal.

    mraSum = sum(mra,1);
max(abs(mraSum-noissin))
    ans = 
1.6591e-12

    Plot the MRA.

    tiledlayout(level+1,1)
for k=1:level
    nexttile
    plot(mra(k,:))
    title("Projection Onto Detail Subspace "+num2str(k))
end
nexttile
plot(mra(end,:))
title("Projection Onto Approximation Subspace")

    Figure contains 4 axes objects. Axes object 1 with title Projection Onto Detail Subspace 1 contains an object of type line. Axes object 2 with title Projection Onto Detail Subspace 2 contains an object of type line. Axes object 3 with title Projection Onto Detail Subspace 3 contains an object of type line. Axes object 4 with title Projection Onto Approximation Subspace contains an object of type line.

    Input Arguments

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    Coefficients to reconstruct, specified as 'a' or 'd', for approximation or detail coefficients, respectively.

    Wavelet decomposition of a 1-D signal, specified as a real-valued vector. The vector contains the wavelet coefficients. The bookkeeping vector l contains the coefficients by level. See wavedec.

    Data Types: double | single

    Bookkeeping vector, specified as a vector of positive integers. The bookkeeping vector is used to parse the coefficients in the wavelet decomposition c by level. See wavedec.

    Data Types: double | single

    Analyzing wavelet used to create the wavelet decomposition structure [c,l], specified as a character vector or string scalar. wrcoef supports only orthogonal or biorthogonal wavelets. See wfilters.

    Wavelet reconstruction filters, specified as a pair of even-length real-valued vectors. LoR is the lowpass reconstruction filter, and HiR is the highpass reconstruction filter. The lengths of LoR and HiR must be equal. See wfilters for additional information.

    Coefficients level, specified as a nonnegative integer. When type is 'a', n is allowed to be 0. Otherwise, n is a strictly positive integer such that n ≤ length(l)-2. The default value of n is length(l)-2.

    Version History

    Introduced before R2006a

    See Also

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