largestr.m

linear time－frequency toolbox

function [xo,N]=largestr(xi,p)
%LARGESTR   Keep largest ratio of coefficients.
%   Usage:  xo=LARGESTR(x,p);
%           [xo,N]=LARGESTR(x,p);
%
%   LARGESTR(x,p) returns an array of the same size as x keeping
%   the fraction p of the coefficients. The largest coefficients
%   are kept.
%
%   [xo,N]=LARGESTR(xi,p) will additionally return the number of
%   coefficients kept.
%
%   Note that if this function is used on coefficients coming from a
%   redundant transform or from a transform where the input signal was
%   padded, the coefficient array will be larger than the original input
%   signal. Therefore, the number of coefficients kept might be higher
%   than expected.
%
%   SEE ALSO:  LARGESTN
%
%   REFERENCES:
%     S. Mallat. A wavelet tour of signal processing. Academic Press, San Diego,
%     CA, 1998.

if nargin~=2
  error('Wrong number of input arguments.');
end;

if (prod(size(p))~=1 || ~isnumeric(p))
  error('p must be a scalar.');
end;

% Determine the size of the array.
ss=prod(size(xi));

N=round(ss*p);

xo=largestn(xi,N);