function [MedFreq,errormsg] = MedianFrequency(xV,leftcutoff,rightcutoff)

% [MedFreq,errormsg] = MedianFrequency(xV,leftcutoff,rightcutoff)

% MEDIANFREQUENCY computes the median frequency in a frequency range given 

% by 'leftcutoff' and 'rightcuroff' for a given time series 'xV'. 

% The standard periodogram is called to compute the power spectrum assuming 

% frequency=1, so that the largest frequency the power spectrum is computed 

% for is 0.5 if 'rightcuroff' is specified. The lower frequency is given 

% by 'leftcutoff' or 0 if 'leftcutoff' is not specified. The frequency 

% resolution is given by the length of the time series. 

% INPUT 

% - xV      : the given time series

% - leftcutoff: the left cutoff of frequency (to avoid the effect of drifts 

%               in the signal).

% - rightcutoff: the right cutoff of frequency (to avoid the effect of  

%                high frequency elements in the signal).

% OUTPUT

% - MedFreq : The median frequency

% - errormsg: a string of error message in case output cannot be generated.

%========================================================================

%     <MedianFrequency.m>, v 1.0 2010/02/11 22:09:14  Kugiumtzis & Tsimpiris

%     This is part of the MATS-Toolkit http://eeganalysis.web.auth.gr/

%========================================================================

% Copyright (C) 2010 by Dimitris Kugiumtzis and Alkiviadis Tsimpiris 

%                       <dkugiu@gen.auth.gr>

%========================================================================

% Version: 1.0

% LICENSE:

%     This program is free software; you can redistribute it and/or modify

%     it under the terms of the GNU General Public License as published by

%     the Free Software Foundation; either version 3 of the License, or

%     any later version.

%

%     This program is distributed in the hope that it will be useful,

%     but WITHOUT ANY WARRANTY; without even the implied warranty of

%     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

%     GNU General Public License for more details.

%

%     You should have received a copy of the GNU General Public License

%     along with this program. If not, see http://www.gnu.org/licenses/>.

%=========================================================================

% Reference : D. Kugiumtzis and A. Tsimpiris, "Measures of Analysis of Time Series (MATS): 

%             A Matlab  Toolkit for Computation of Multiple Measures on Time Series Data Bases",

%             Journal of Statistical Software, in press, 2010

% Link      : http://eeganalysis.web.auth.gr/

%========================================================================= 

if nargin==2

    rightcutoff = 0.5;

elseif nargin==1

    rightcutoff = 0.5;

    leftcutoff = 0.0;

end

errormsg = [];

[psV,freqV]=periodogram(xV); 

MedFreq = [];

if length((find(isnan(psV))))==0

    d=length(psV(find(freqV<leftcutoff)));

    op=find(cumsum(psV(find(freqV>=leftcutoff)))>0.5*sum(psV(find(freqV>=leftcutoff & freqV<=rightcutoff))));

    if length(op)>0

        MedFreq=freqV(op(1)+d);

    end

else

    errormsg = 'The periodogram could not be computed or cutoff values are not proper.';

end