function [energy, level] = energyatlevel(w)
% FUNCTION:    energyatlevel      Part of DPWT toolbox.
%
% SYNOPSIS:    [LEVEL, ENERGY] = energyatlevel(W)
%
% DESCRIPTION: energyatlevel determines the energy (sum 
%              of the squares of the coefficients) at each
%              level of the wavelet coefficient vector W. 
%              The output column vectors
%              'level' and 'energy' contain the level numbers
%              and corresponding energy values.
%
% EXAMPLE:  f = sin(1*2*pi*exp(2.5*[0:(2^7 - 1)].^1.03 ...
%                   / 2^7) ...
%               )';
%           w = dpwt(f,daubcofs(3));
%           [energy, level] = energyatlevel(w);
%           discreteplot(level,energy),
%           xlabel('level'),
%           ylabel('energy')

%
% AUTHOR: Neil Getz
% DATE: 5-5-92
%
% COPYRIGHT 1992, Neil Getz
%

if(( nargin < 1 )|( nargin > 2 )),
  help energyatlevel;
  return;
end

p = log( length(w) )/log(2);
energy = zeros( p+1, 1 ); % for size
level = energy; % for size
for i = -1:(p-1),
  level( i + 2 ) = i;
  energy( i + 2 ) = sum( getlevel( w, i).^2);
end

if( nargin == 2 )
  axis([-1 (p-1) 0 1.1*max(energy)]);
  discreteplot( level, energy);
  xlabel( 'level' );
  ylabel( 'Energy' );
  axis;
end