yn=isfibonacci(fn)

%ISFIBONACCI Determine if a given number is a Fibonacci number.
%
%   Given a number F this function returns 1 if the number F is a Fibonacci
%   number and 0 if it is not.  
%
%      IS = ISFIBONACCI(FN);
%
%See also FIBONACCI, IFIBONACCI

% $Author: graceej $ $Date: 2009/10/24 11:08:05 $
% $Revision: 1.3 $


% Copyright (c) 2009, Edward J. Grace
% All rights reserved.
 
% Redistribution and use in source and binary forms, with or 
% without modification, are permitted provided that the following 
% conditions are met:
 
%     * Redistributions of source code must retain the above 
%       copyright notice, this list of conditions and the following 
%       disclaimer.
%     * Redistributions in binary form must reproduce the above 
%       copyright notice, this list of conditions and the following 
%       disclaimer in the documentation and/or other materials 
%       provided with the distribution.
%     * Neither the name of the Imperial College London nor the 
%       names of its contributors may be used to endorse or 
%       promote products derived  this software without specific 
%       prior written permission.
 
% THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND 
% CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, 
% INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF 
% MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE 
% DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS 
% BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, 
% EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED 
% TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 
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function yn=isfibonacci(fn)
pos=sqrt(5*fn.^2+4);
neg=sqrt(5*fn.^2-4);
pos=pos-fix(pos)==zeros(size(pos));
neg=neg-fix(neg)==zeros(size(pos));
yn = or(pos,neg);

%% CVS Log
% 
% $Log: isfibonacci.m,v $
% Revision 1.3  2009/10/24 11:08:05  graceej
% * Modified license to make use of the current BSD style open source initiative license.
%
% Revision 1.2  2009/05/06 20:09:45  graceej
% * Updated make package target to include distribution of the license file and README.
%
% Revision 1.1  2009/04/17 11:42:32  graceej
% * Brought over auto_checking/BPC-LIB tag=end and checked in.
% * This old repository is now defunct.
%
% Revision 1.2  2009/04/17 11:37:26  graceej
% * Wholescale modification of the entire library.
%
% Revision 1.1.2.1  2008/09/16 13:59:44  graceej
% * Initial checkin.
%
%