%% Simulate the Total Return of a Bond Portfolio Until Maturity
% Define the zero curve data.

Settle = datenum('4-Apr-2016');
ZeroTimes = [3/12 6/12 1 5 7 10 20 30]';
ZeroRates = [-0.01 -0.009 -0.0075 -0.003 -0.002 -0.001 0.002 0.0075]';
ZeroDates = datemnth(Settle,ZeroTimes*12);
RateSpec = intenvset('StartDates', Settle,'EndDates', ZeroDates, 'Rates', ZeroRates)

%
% Define the bond parameters for the five bonds in the portfolio.

Maturity = datemnth(Settle,12*5);  % All bonds have the same maturity
CouponRate = [0.035;0.04;0.02;0.015;0.042];  % Different coupon rates for the bonds
nBonds = length(CouponRate);

%
% Define the Hull-White parameters.

alpha = .1;
sigma = .01;
HW1F = HullWhite1F(RateSpec,alpha,sigma)

%
% Define the simulation parameters.

nTrials = 1000;
nPeriods = 12*5;
deltaTime = 1/12;
SimZeroCurvePaths = simTermStructs(HW1F, nPeriods,'nTrials',nTrials,'deltaTime',deltaTime);
SimDates = datemnth(Settle,1:nPeriods);

%
% Preallocate and initialize for the simulation.

SimBondPrice = zeros(nPeriods+1,nBonds,nTrials);
SimBondPrice(1,:,:) = repmat(bondbyzero(RateSpec,CouponRate,Settle,Maturity)',[1 1 nTrials]);
SimBondPrice(end,:,:) = 100;

[BondCF,BondCFDates,~,CFlowFlags] = cfamounts(CouponRate,Settle,Maturity);
BondCF(CFlowFlags == 4) = BondCF(CFlowFlags == 4) - 100;
SimBondCF = zeros(nPeriods+1,nBonds,nTrials);

%
% Compute bond values for each simulation date and path. Note that you can vectorize over the trial dimension.

for periodidx=1:nPeriods
    if periodidx < nPeriods
        simRateSpec = intenvset('StartDate',SimDates(periodidx),'EndDates',...
            datemnth(SimDates(periodidx),ZeroTimes*12),'Rates',squeeze(SimZeroCurvePaths(periodidx+1,:,:)));
        SimBondPrice(periodidx+1,:,:) = bondbyzero(simRateSpec,CouponRate,SimDates(periodidx),Maturity);
    end
    
    simidx = SimDates(periodidx) == BondCFDates;
    SimCF = zeros(1,nBonds);
    SimCF(any(simidx,2)) = BondCF(simidx);
    ReinvestRate = 1 + SimZeroCurvePaths(periodidx+1,1,:);
    SimBondCF(periodidx+1,:,:) = bsxfun(@times,bsxfun(@plus,SimBondCF(periodidx,:,:),SimCF),ReinvestRate);
end

%
% Compute the total return series.

TotalCF = SimBondPrice + SimBondCF;

%
% Assume the bond portfolio is equally weighted and plot the simulated bond portfolio returns.

TotalCF = squeeze(sum(TotalCF,2));

TotRetSeries = bsxfun(@rdivide,TotalCF(2:end,:),TotalCF(1,:)) - 1;
plot(SimDates,TotRetSeries)
datetick
ylabel('Bond Portfolio Returns')
xlabel('Simulation Dates')
title('Simulated Bond Portfolio Returns')

% Copyright 2012 The MathWorks, Inc.