simulback.m

计算VaR的

function [sn,svar,vp] = simulback(X,RF,RC,legame,valuta,vm,p,rendimento,tipo,campione,dati,lambda,datidelta)

%SIMULBACK	baktesting for hystorical simulation VaR.
%
%	[sn,svar,vp] = simulback(X,RF,RC,legame,valuta,vm,p,rendimento,tipo,campione,dati,lambda,datidelta) 
%	calculates the number of outlier in portfolio backtesting for VaR with
%	historical simulation method. Campione represents the number of simulations (for
%	Basel is 250) and dati is the number of data used for VaR calculation.
%	Lambda is the weight in EWMA volatility forecast.
%   If Datidelta = 0 the mapping procedure is calculated over all X,
%   = 1 only with defined data.
%
%	All data must be in columns.
%

%	Copyright (c) 2004 by Flavio Bazzana
%   Department of Computer and Management Sciences
%   University of Trento
%   38100 - Trento ITALY
%   [e-mail]

n=size(X,1);
m=length(valuta);
[DX,DR,cambi,fattori,prezzi] = rendimenti(X,RF,RC,rendimento);
[deltax,dev,cor,C] = semplicecorr(DX,DR,legame);
cp = vm./prezzi;

for i=1:campione+1

% VaR interval

	X1=X(n-dati-i:n-i,:);
	RF1=RF(n-dati-i:n-i,:);
	RC1=RC(n-dati-i:n-i,:);
	
% calculation of simulvar over such interval
	
	[DX,DR,cambi,fattori,prezzi] = rendimenti(X1,RF1,RC1,rendimento);
	if lambda==1
		[delta,dev,cor,C] = semplicecorr(DX,DR,legame);
		else [delta,dev,cor,C] = ewmacorr(DX,DR,legame,lambda);
	end
	if datidelta==1
		[svar(i)] = simulvar(DR,RC1,X1,delta,valuta,legame,vm,1,p,tipo,rendimento);
		else [svar(i)] = simulvar(DR,RC1,X1,deltax,valuta,legame,vm,1,p,tipo,rendimento);
	end

% calculation of portfolio value
	
	for j=1:m
		if valuta(j)==0
			k1(j)=1;
			else k1(j)=cambi(valuta(j));
		end
	end
	k2 = prezzi.*k1';
	vp(i) = k2'*cp;

end

% calculation of the exceptions

sn=0;
for i=1:campione
	if vp(i+1)-vp(i)<-svar(i)
		sn=sn+1;
	end
	if vp(i+1)-vp(i)>svar(i)
		sn=sn+1;
	end
end

f=1:campione;
plot(f,-svar(1:campione),'b',f,svar(1:campione),'b',f,diff(vp),'r')
title('Backtesting of historical VaR simulation')
xlabel('Sample')
ylabel('VaR')