function [E,V]=dpss(N, W, method, int, size) 
 
% Syntax: [E,V]=dpss(N, W); [E,V]=dpss(N, W, method, int, size) 
% Dpss generates discrete prolate spheroidal  
% sequences of length N for window width W. 
% W should be 2, 5/2, 3, 7/2, 4, etc. 
% 
% Returns: E: matrix of the first 2W eigenvectors 
%          V: vector of the first 2W eigenvalues. 
%  
% If only N and W are given, dpss first looks for a dpss 
% file on disk. If this is not found, the dpss are generated 
% by spline interpolation from dpss of length 256. If these 
% are not found, the dpss are calculated directly. 
% 
% These defaults can be overridden by the other arguments: 
% 
% 'Method' should be either 'calc' or 'terp'. 
%     'calc': Compute the dpss using dpsscalc.m; 
%     'terp': Interpolate new dpss from existing 
%             ones using dpssint.m. 
% Interpolation is significantly faster than calculation. 
% 
% If 'terp' is specified, the interpolation method 'int'  
% can be specified as 'linear' or 'spline' (the default). 
% Linear is faster, but splining is slightly better. 
% 
% The size of the dpss to be used in the interpolation can 
% be specified in 'size' - these dpss must be stored on disk. 
% The default is 256.  
% 
% For further details, see dpsscalc.m and dpssint.m. 
% 
% Written by Eric Breitenberger, version date 10/3/95. 
% Please send comments and suggestions to eric@gi.alaska.edu 
% 
 
if nargin==2 
  if rem(W,1)==0 
    filename=['s' int2str(N) '_' int2str(W) '.mat'];  
  else 
    filename=['s' int2str(N) '_' int2str(10*W) '.mat'];  
  end 
 
  if exist(filename)==2 
    msg=['Loading the DPSS from disk...'];  
    disp(msg) 
    eval(['load ' filename]) 
  else 
    if rem(W,1)==0 
      filename=['s' int2str(256) '_' int2str(W) '.mat'];  
    else 
      filename=['s' int2str(256) '_' int2str(10*W) '.mat'];  
    end 
    if exist(filename)==2 
      disp('Interpolating the DPSS ...') 
      [E,V]=dpssint(N,W); 
    else 
      disp('Calculating the DPSS ...') 
      [E,V]=dpsscalc(N,W); 
    end 
  end 
 
elseif nargin==3  
  if isstr(method) 
    if length(method)==6 
      msg=['Computing the DPSS using ' method ' interpolation...'];  
      disp(msg) 
      [E,V]=dpssint(N,W,method); 
    elseif length(method)==4 
      if method=='calc' 
        msg=['Computing the DPSS using direct calculation...'];  
        disp(msg) 
        [E,V]=dpsscalc(N,W); 
      elseif method=='terp' 
        disp('Interpolating the DPSS ...') 
        [E,V]=dpssint(N,W); 
      else 
        error('Improper specification of arguments.') 
      end 
    end 
  else 
    msg=['Computing DPSS using spline interpolation, size ' int2str(method) '...']; 
    disp(msg) 
    [E,V]=dpssint(N,W,method); 
  end 
 
elseif nargin==4 
  if length(method)==6 
    msg=['Computing the DPSS using ' method ' interpolation, size ' int2str(int) '...'];  
    disp(msg) 
    [E,V]=dpssint(N,W,int,method); 
  else 
    error('Improper specification of arguments.') 
  end 
 
else 
  msg=['Computing the DPSS using ' int ' interpolation, size ' int2str(size) '...'];  
  disp(msg) 
  [E,V]=dpssint(N,W,size,int); 
end 
 
k=2*W;  % Return only first k values 
E=E(:,1:k); 
V=V(1:k);