fibonacci(n)

function y = fibonacci(n)
% FIBONACCI fibonacci numbers.
%
%  FIBONACCI(N) for scalar N, is the N-th fibonacci number. When N is an N-D
%  array, FIBONACCI(N) is the array of fibonacci numbers corresponding to
%  each element of N.
%
% Example:
% >> fibonacci(magic(3))
% 
% ans =
% 
%     21     1     8
%      2     5    13
%      3    34     1
% 
% >> fibonacci(-pascal(3))
% 
% ans =
% 
%      1     1     1
%      1    -1     2
%      1     2    -8
% 
% >> 

% Mukhtar Ullah
% [e-mail]
% May 24, 2005

if any(floor(n(:)) ~= n(:)) || ~isreal(n(:))
  error('N must be an array of integers.')
end

sqrt5 = sqrt(5);
m = (1 + sqrt5)/2;
y = zeros(size(n));
i = n~=0;
y(i) = round(m.^abs(n(i))/sqrt5);
k = rem(n+1,2)<0;
y(k) = -y(k);