roundd(X,N)

function Y = roundd(X,N)
% ROUNDD   Rounds to some digits from the left.
%   Y = ROUNDD(X,N) rounds the array X up to N digits from the left, taking
%   the element with more digits to the left as the reference, even if it 
%   is a decimal.
%
%   Example: 
%      If X = [ 1234.56 25.5 0.045 856 52.87], 
%      then roundd(X,2) = [1200 0 0 900 100].
%
%   See also ROUND, ROUNDN

%   Written by
%   M.S. Carlos Adrin Vargas Aguilera
%   Physical Oceanography PhD candidate
%   CICESE 
%   Mexico, november 2006
% 
%   [e-mail]

% Make sure input is an integer:
if any([~isnatural(N(:)); (numel(N)~=1); (N(:)<1)])
 error('Argument must be an integer.')
end

N = N-1;
Xmax = max(abs(X(:)));
if Xmax ~= 0
 M = floor(log10(Xmax));
 Y = X*10^(N-M);
 Y = round(Y);
 Y = Y*10^(M-N);
else
 Y = X;
end


function yes = isnatural(n)
%ISNATURAL   Checks if an array has natural numbers.
%   Y = ARENATURAL(X) returns an array of the same size as X with ones in
%   the elements of X that are natural numbers (...-2,-1,0,1,2,...), and 
%   zeros where not.

%   Written by
%   M.S. Carlos Adrin Vargas Aguilera
%   Physical Oceanography PhD candidate
%   CICESE 
%   Mexico, november 2006
% 
%   [e-mail]

yes = (n==floor(n)).*(isreal(n));

% Carlos Adrin. [e-mail]