Wavelet Toolbox™

Compute local maxima positions

Syntax

• [Y,I] = localmax(X,ROWINIT,REGFLAG)
  [Y,I] = localmax(X,ROWINIT)
  [Y,I] = localmax(X)
  

Description

For a matrix X, localmax computes and chains the local maxima along the rows.

The default values are ROWINIT = size(X,1) and REGFLAG = true.

First, localmax computes the local maxima positions on each row of X. Then, starting from the row (ROWINIT-1), localmax chains the maxima positions along the columns. If p0 is a local maxima position on the row R0, then p0 is linked to the nearest maxima position on the row R0+1.

Y is a matrix of the same size of X such that:

• When R = ROWINIT, then, if X(ROWINIT,j) is a local maximum, Y(ROWINIT,j) = j and otherwise, Y(ROWINIT,j) = 0,.
• When R < ROWINIT, if X(R,j) is not a local maximum then Y(R,j) = 0.
• Otherwise if X(R,j) is a local maximum, then Y(R,j) = k, where k is such that X(R+1,k) is a local maximum and k is the nearest position of j.

I contains the indices of nonzero values of Y.

If REGFLAG = true, S = X(ROWINIT,:) is first regularized using the wavelet 'sym4'. Instead of S, the approximation of level 5 is used to start the algorithm.

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