function theDateNum = EP_DateNum(theEpicTime)

% EP_DateNum -- Matlab date-number from epic-time.
%  EP_DateNum(theEpicTime) returns the Matlab date-number
%   for theEpicTime (expressed as two-columns [time time2]).
%   The "time2" component defaults to 0.  See the Matlab
%   "datenum()" function.
%  EP_DateNum('demo') demonstrates itself.
%  EP_DateNum (no argument) shows "help" and demonstrates itself.


%%% START USGS BOILERPLATE -------------% There is no published documentation for these programs- use the 
%  internal comments and help function.
% Programs written in Matlab- as early as 7.2.0.232 (R2006a) and 
% most recent modifications in  v7.8.0 (R2009a)
% Programs ran on PC with Windows XP Professional OS, and RHEL4 linux.
%
% "Although this program has been used by the USGS, no warranty, 
% expressed or implied, is made by the USGS or the United States 
% Government as to the accuracy and functioning of the program 
% and related program material nor shall the fact of distribution 
% constitute any such warranty, and no responsibility is assumed 
% by the USGS in connection therewith."
%%% END USGS BOILERPLATE --------------

  
% Copyright (C) 1997 Dr. Charles R. Denham, ZYDECO.
%  All Rights Reserved.
%   Disclosure without explicit written consent from the
%    copyright owner does not constitute publication.
 
% Version of 01-Jul-1997 15:54:18.

% Note: May 23, 1968 = Julian Day 2,440,000.

if nargin < 1, help(mfilename), theEpicTime = 'demo'; end

if strcmp(theEpicTime, 'demo')
   theEpicTime = [2440000 0];
   if exist('begets')
      begets('EP_DateNum', 1, theEpicTime, ep_datenum(theEpicTime))
     else
      disp([' ## EP_DateNum(' mat2str(theEpicTime) ') ==> '  ep_datenum(theEpicTime) ])
   end
   return
end

MSEC_PER_DAY = 24*60*60*1000;

% We expect two-columns [time time2].

[m, n] = size(theEpicTime);
if n < 2, theEpicTime(:, 2) = 0; end

[m, n] = size(theEpicTime);
if m == 2 & n ~= 2
    theEpicTime = theEpicTime.';
end

theEpicTime = theEpicTime(:, 1:2) * [1.0; 1.0/MSEC_PER_DAY];

t0 = datenum(1968, 5, 23) - 2440000;   % May 23, 1968.
t = theEpicTime + t0;

if nargout > 0
   theDateNum = t;
  else
   disp(t)
end