function hh = xerrorbar(x, y, l,u,symbol)

%XERRORBAR Error bar plot.

%

%   XERRORBAR(X,Y,L,U) behaves similar to ERRORBAR, from which it was 

%   derived

%

%   Global Variables:

%	TICSLEN		half-length of ticmarks in terms of y units;

%			+ve values: y units; 

%			-ve values: fraction of y total y-range;

%			default: -0.005

%	ERRORBARS_ONLY	do not plot data points

%======================================================================

%                    X E R R O R B A R . M 

%                    doc: Sun Feb 23 08:55:37 2003

%                    dlm: Tue Mar 11 11:52:52 2003

%                    (c) 2003 Mathworks; changes by A.M. Thurnherr

%                    uE-Info: 137 49 NIL 0 0 72 2 2 8 NIL ofnI

%======================================================================

% HISTORY:

%	Feb 23, 2003: - created from [errorbar.m]

%	Mar 10, 2003: - added TICSLEN

%	Mar 11, 2003: - changed TICSLEN sign convention

%		      - added ERRORBARS_ONLY

global TICSLEN; if isempty(TICSLEN), TICSLEN = -0.005; end

global ERRORBARS_ONLY;

if min(size(y))==1,

  npt = length(y);

  x = x(:);

  y = y(:);

    if nargin > 2,

        if ~isstr(l),  

            l = l(:);

        end

        if nargin > 3

            if ~isstr(u)

                u = u(:);

            end

        end

    end

else

  [npt,n] = size(y);

end

if nargin == 3

    if ~isstr(l)  

        u = l;

        symbol = '-';

    else

        symbol = l;

        l = x;

        u = x;

        x = y;

        [m,n] = size(x);

        y(:) = (1:npt)'*ones(1,n);;

    end

end

if nargin == 4

    if isstr(u),    

        symbol = u;

        u = l;

    else

        symbol = '-';

    end

end

if nargin == 2

    l = x;

    u = x;

    x = y;

    [m,n] = size(x);

    y(:) = (1:npt)'*ones(1,n);;

    symbol = '-';

end

u = abs(u);

l = abs(l);

if isstr(x) | isstr(y) | isstr(u) | isstr(l)

    error('Arguments must be numeric.')

end

if ~isequal(size(x),size(y)) | ~isequal(size(x),size(l)) | ~isequal(size(x),size(u)),

  error('The sizes of X, Y, L and U must be the same.');

end

if TICSLEN < 0

	tee = (max(y(:))-min(y(:))).*-TICSLEN;

else

	tee = TICSLEN;

end

yl = y - tee;

yr = y + tee;

xtop = x + u;

xbot = x - l;

n = size(x,2);

% Plot graph and bars

hold_state = ishold;

cax = newplot;

next = lower(get(cax,'NextPlot'));

% build up nan-separated vector for bars

yb = zeros(npt*9,n);

yb(1:9:end,:) = y;

yb(2:9:end,:) = y;

yb(3:9:end,:) = NaN;

yb(4:9:end,:) = yl;

yb(5:9:end,:) = yr;

yb(6:9:end,:) = NaN;

yb(7:9:end,:) = yl;

yb(8:9:end,:) = yr;

yb(9:9:end,:) = NaN;

xb = zeros(npt*9,n);

xb(1:9:end,:) = xtop;

xb(2:9:end,:) = xbot;

xb(3:9:end,:) = NaN;

xb(4:9:end,:) = xtop;

xb(5:9:end,:) = xtop;

xb(6:9:end,:) = NaN;

xb(7:9:end,:) = xbot;

xb(8:9:end,:) = xbot;

xb(9:9:end,:) = NaN;

[ls,col,mark,msg] = colstyle(symbol); if ~isempty(msg), error(msg); end

symbol = [ls mark col]; % Use marker only on data part

esymbol = ['-' col]; % Make sure bars are solid

h = plot(xb,yb,esymbol); hold on

if ~ERRORBARS_ONLY, h = [h;plot(x,y,symbol)]; end

if ~hold_state, hold off; end

if nargout>0, hh = h; end