appcoef

Purpose

1-D approximation coefficients

Syntax

• A = appcoef(C,L,'wname',N)
  A = appcoef(C,L,'wname')
  A = appcoef(C,L,Lo_R,Hi_R)
  A = appcoef(C,L,Lo_R,Hi_R,N)
  

Description

appcoef is a one-dimensional wavelet analysis function.

appcoef computes the approximation coefficients of a one-dimensional signal.

A = appcoef(C,L,'wname',N) computes the approximation coefficients at level N using the wavelet decomposition structure [C,L] (see wavedec for more information).

'wname' is a string containing the wavelet name. Level N must be an integer such that 0 N length(L)-2.

A = appcoef(C,L,'wname') extracts the approximation coefficients at the last level: length(L)-2.

Instead of giving the wavelet name, you can give the filters.

For A = appcoef(C,L,Lo_R,Hi_R) or A = appcoef(C,L,Lo_R,Hi_R,N), Lo_R is the reconstruction low-pass filter and Hi_R is the reconstruction high-pass filter (see wfilters for more information).

Examples

• % The current extension mode is zero-padding (see dwtmode).
  
  % Load a one-dimensional signal. 
  load leleccum; s = leleccum(1:3920); 
  
  % Perform decomposition at level 3 of s using db1. 
  [c,l] = wavedec(s,3,'db1');
  
  % Extract approximation coefficients at level 3, from the 
  % wavelet decomposition structure [c,l]. 
  ca3 = appcoef(c,l,'db1',3);
  % Using some plotting commands,
  % the following figure is generated.
  
  
  

Algorithm

The input vectors C and L contain all the information about the signal decomposition.

Let NMAX = length(L)-2; then C = [A(NMAX) D(NMAX) ... D(1)] where A and the D are vectors.

If N = NMAX, then a simple extraction is done; otherwise, appcoef computes iteratively the approximation coefficients using the inverse wavelet transform.

See Also

detcoef, wavedec

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