ema=Xmovavg(asset,windowlength)

function ema=Xmovavg(asset,windowlength)
%Syntax: ema=Xmovavg(asset,windowlength)
%_______________________________________
%
% Calculates the Exponential Moving Average of a financial time series. It
% can also plot its chart.
%
% ema is the exponential moving average.
% asset is the security data.
% windowlength is the length of the time window.
%
%
% Reference:
% Adapted from Trey Johnson's C/C++ code. Thanks Trey, you have done a great
% job!!!
%
%
% Alexandros Leontitsis
% Department of Education
% University of Ioannina
% 45110 - Dourouti
% Ioannina
% Greece
%
% University e-mail: [e-mail]
% Lifetime e-mail: [e-mail]
% Homepage: http://www.geocities.com/CapeCanaveral/Lab/1421
%
% 16 December 2003.

if nargin<1 | isempty(asset)==1
    error('You should provide a time series.');
else
    % asset must be a vector
    if min(size(asset))>1
        error('Invalid time series.');
    end
    asset=asset(:);
end

if nargin<2 | isempty(windowlength)==1
    windowlength=4;
else
    % windowlength must be scalar
    if sum(size(windowlength))>2
        error('windowlength must be scalar.');
    end
    % windowlength must be an integer
    if round(windowlength)-windowlength~=0
        error('windowlength must be an integer.');
    end
    % windowlength must be greater than or equal to 2
    if windowlength<2
        error('windowlength must be greater than or equal to 2');
    end
end


% Calculate the Exponential Moving Average factor
fac=2/(1+windowlength);

% Initialize the loop
sum1=0;
sum2=0;

for i=windowlength+1:length(asset)
    
    sum1=sum1+fac*(asset(i)-sum1);
    sum2=sum2+fac*(1-sum2);
    
    % Calculate the Exponential Moving Agerage
    ema(i-windowlength,1)=sum1/sum2;
    
end

if nargout==0
    % If there are no output arguments, make a plot
    r=length(asset);
    rema=length(ema);
    plot(1:r,asset,(r-rema+1:r),ema)
end