function [] = bihist(x1,x2,n)
% BIHIST(X1,X2,N) open a new figure an plot a back to back histogram
% X1: variable 1 (right side, colour blue)
% X2: variable 2 (right side, colour green)
% n : number of classes for each histogramm
% make two dummy-histogram
[temp, d1] = hist(x1,n); %#ok<ASGLU>
[temp, d2] = hist(x2,n); %#ok<ASGLU>
clear temp
% calculate classes
d = min([d1 d2]):((max([d1 d2])-min([d1 d2]))/(n-1)) : max([d1 d2]);
% create the two histograms
templ = hist(x1,d);
tempr = hist(x2,d);
% scaling the histograms
templ=templ*-1;
% create bar plot
left=barh(templ,'style','hist');
hold on
right = barh(tempr,'style','hist');
plot([0 0], [1 n],'k')
% change color of left histogram
set(left,'FaceColor',[0 0 1]);
% change color of right histogram
set(right,'FaceColor',[0 1 0]);
% distance factor to frame
dt=1.2;
xlim([-max(abs([templ tempr]))*dt max(abs([templ tempr]))*dt])
% mark the y-axis
yl = get(gca,'YTick');
b = (max(d)-min(d))/(n-1);
a = max(d)-b*n;
yl2 = yl*b+a;
ds = cell(size(yl2));
for k=1:length(yl2)
ds{k} = num2str(yl2(k),3);
end
set(gca,'YTickLabel',ds)
% rewrite the x-axis with positiv values
xl = get(gca,'XTickLabel');
xl = regexprep(cellstr(xl),'-','');
set(gca,'XTickLabel',regexprep(cellstr(xl),'-',''))
