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Risk-neutral density recovery via spectral analysis

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Risk-neutral density recovery via spectral analysis

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Implementation of Monnier (2013) "RND recovery via spectral analysis"

spectralrecovery(X,bid,ask,F,r,tau,nopt)
function out = spectralrecovery(X,bid,ask,F,r,tau,nopt)
%SPECTRALRECOVERY Recover option implied risk-neutral density. (***)
%   OUT = SPECTRALRECOVERY(X,bid,ask,F,r,tau)
%   OUT = SPECTRALRECOVERY(X,bid,ask,F,r,tau,nopt)
%
%   Inputs:
%   X   [nx1]   Strike prices
%   bid [nx1]   Put option bid quotes , corresponding to X
%   ask [nx1]   Put option ask quotes,  corresponding to X
%   F   [1x1]   Futures price
%   r   [1x1]   Risk-free rate of interest (continuously compounded)
%   tau [1x1]   Time to maturity of the option set
%   nopt        Optimal: User provided spectral cutoff value. 
%
% If no predetermined spectral cutoff value is supplied, the program
% searches for the smallest value N for which the algorithm yields a
% feasible result.
%
%   OUT contains
%   .N          Smallest spectral cutoff for which all constraints hold
%   .X          'Dense' strike grid [0,1,2,...,floor(B),B], B=2*F.
%   .densityX   Implied risk-neutral density for each point in X
%   .returns    'Dense' return grid [-log(2):0.001:log(2)]
%   .densityR   Implied risk-neutral density for each point in RETURNS
%   .prices     'Dense' put option prices for each point in X
%   .POINTS     Index vector of points with bid/ask provided.
%
% The spectral recovery method of Monnier (2013) takes available put option 
% bid/ask quotes and estimates the smoothest RND compatible with the quotes
%
% (***)Monnier (2013)"Risk-neutral density recovery via spectral analysis"
%
%   Matthias Held, matthias.held@whu.edu
%   $Date: 2013/03/18$
% 

% prepare solver
options = optimset( 'Algorithm','interior-point-convex', ...
                    'MaxIter',175,'TolFun',1E-8,'TolX',1E-8 , ...
                    'TolCon',1E-8, 'Display','none');
% reshape and prepare input data, sort by strike price
if nargin==6; nopt = [];end %
if size(X,2)>size(X,1); X=X'; end
if size(bid,2)>size(bid,1); bid=bid'; end
if size(ask,2)>size(ask,1); ask=ask'; end
temp        = sortrows([X bid ask],1);
X           = temp(:,1);
bid         = temp(:,2);
ask         = temp(:,3);
clear temp;
% choice of B
% set the cutoff strike B. "The higher the B, the higher we will need to go
% into the spectrum of gamma* [the put operator] since the smoothest RND
% that fits the dataw ill be more and more concentrated around the center
% of the intervall I=[0,B]." Monnier (2003), p. 21.
B           = ceil(2*F);
xi          = [0:1:B]';
% Set the 'dense' strike grid xi
% find those 'dense' strikes xi for which put quotes are observed, 
% augment ask quotes for strike zero (P(0)=0) and for strike B.
n           = length(xi);
xiBid       = find(ismember(xi,X));
xiAsk       = [1 ; xiBid ; n];
ask         = [0 ; ask ; ask(end)+exp(-r*tau)*(xi(end)-X(end))];
% Iterate on N via Bisection method. Under 15 or so steps should suffice
if isempty(nopt)
    NLeft   = 4;        %
    NRight  = 200;      % maximum 200 (see beta function below)
    Nwork   = NRight;   %
    omHatR   = 0; exR=-5;
else
    NLeft   = nopt;     
    NRight  = nopt;
end
brSwitch    = 0;
for kLoop = 1:20        % 15 steps should be enough, I guess
    N   = round(0.5*(NLeft+NRight));
    % Bisection method applies only without nopt supplied by user.
    if isempty(nopt)&(NRight==N)&(N~=200)
        % reuse results from last step to save one iteration.
        omHat   = omHatR;exitflag= exR;break; 
    end

    if N==200
        brSwitch=1;
    end
        
    % Setup linear inequality and equality matrices
    % Ineqal: bid <= P <= ask; P(0) <= 0; P(B) <= ask(end)+df*(B-X(end));
    % P(.) is convex and incraesing.
    % Eqal: q(0)=0, sum(q.*xi)=F
    Omat    = omegaMatrix(N,B);             % matrix of inverted lambdas
    phi2Temp= phi2(N,xi,B);                 % pricing matrix
                                            % phi2Temp*omega_star = P(xi)

    % Aieq<=bieq
    Aieq    = [  phi2Temp(xiAsk,:);         % P(.) <=
                -phi2Temp(xiBid,:);         % -P(.)<=
                 A(xi)*phi2Temp];           % convex, increasing
    bieq    = [ask ; -bid ; b(xi,r,tau,F)]; % (ask,-bid,convex/increas.)'
    % Aeq=beq
    Aeq     = psi([0:N],0,B)*Omat;          % q(0) =
    beq     = 0;                            %       0
    Aeq     = [ Aeq ;                       % sum(q.*xi) = 
                exp(r*tau)*xi'*(psi2(N,xi,B)*Omat)];
    beq     = [beq ; F];                    %             F
    
    % solve quadratic program
    [omHat, ~ , exitflag] = quadprog( Omat^4,zeros(N+1,1),...
                                                    Aieq,bieq,Aeq,beq,...
                                                    [],[],[],options);
    % convergence / choice of next N value
    % if N=Nopt is supplied, stop the loop. 
    if ~isempty(nopt); break;  end
    % if convergence at N, enter left bracket, else right bracket
    if brSwitch ==1
        break;
    end
    
    
    if exitflag==1;
        NRight  = N;
        omHatR  = omHat;
        exR     = exitflag;
    else;
        NLeft=N;
    end        
end
% normalized return density estimation, cutoff at +/- 50 % return
StDiv       = exp(-r*tau)*F;
dRet        = 0.001;
RetHi       = floor(log(2)/dRet)*dRet;
RetLo       = -RetHi;
Ret         = [RetLo:dRet:RetHi]';
qRet        = q(omHat,r,tau,StDiv.*exp(Ret),B).*StDiv.*exp(Ret)*dRet;
% submit output structure fields
out.exitflag=exitflag;
out.N       = N;
out.X       = xi;
out.densityX= q(omHat,r,tau,xi,B);
out.returns = Ret;
out.densityR= qRet;
out.prices  = P(omHat,xi,B);
out.points = xiBid;
end
% Linear inequality Aieq*m<=bieq of quadratic program
function out = A(xi)
% A(xi)*model_prices<=b(xi,r,tau,F) 
% ensures that the resulting put option prices are convex and increasing 
% in the strike xi.
N   = length(xi);
T               = zeros(2*N,N);
T(1:N-2,:)      = T(1:N-2,:) + ...
                    [-diag(1./(xi(2:end-1)-xi(1:end-2))) zeros(N-2,2)];
T(1:N-2,:)      = T(1:N-2,:) + ...
                    [zeros(N-2,1) ...
                    diag(   1./(xi(2:end-1)-xi(1:end-2)) + ...
                            1./(xi(3:end)-xi(2:end-1)) ) ...
                    zeros(N-2,1)];
T(1:N-2,:)      = T(1:N-2,:) + ...
                    [zeros(N-2,2) diag(-1./(xi(3:end)-xi(2:end-1)))];
T(N-1:2*N-2,:)  = diag(-ones(N,1));
T(2*N-1,N-1)    = -1/(xi(N)-xi(N-1));
T(2*N-1,N)      = 1/(xi(N)-xi(N-1));
T(2*N,1)        = 1;
T(2*N,2)        = -1;
out=T;
end
function out = b(xi,r,tau,F)
% A(xi)*model_prices<=b(xi,r,tau,F) 
% ensures that the resulting put option prices are convex and increasing 
% in the strike xi.
N               =length(xi);
c               = zeros(2*N,1);
c(1:N-2)        = 0;                            % convexity 
c(N-1:2*N-2)    = -max(exp(-r*tau)*(xi-F),0);   %df*[xi-F]+ < P,forall xi
c(2*N-1)        = exp(-r*tau);                  % P(B)-P(B-1) < df
c(2*N)          = 0;                            % P(0)-P(1)   < 0
out             = c;
end
% Pricing and density
function out = P(omega,xi,B)
% Pricing function. Using some input vector omega which is of length N,
% this function computes the model implied prices of options with strikes
% in xi using the equations in section 7.4 of Monnier's paper, p. 19.
N = length(omega)-1;
lx = length(xi);
out=zeros(lx,1);
for l=1:lx
    out(l) = sum(omega.*phi([0:N]',xi(l),B));
end
end
function out = q(omega,r,tau,xi,B)
% Density function. Using some input vector omega of length N, q yields 
% the option implied risk-neutral probability density at each strike 
% in xi, using the equations in section 7.4 of Monnier's paper, p. 19.
N=length(omega)-1;
lx = length(xi);
out=zeros(lx,1);
for l=1:lx
out(l) =exp(r*tau)*sum(lambda([0:N]',B).^(-1).*omega.*psi([0:N]',xi(l),B));    
end
end        

% smoothness matrix
function out = omegaMatrix(N,B)
% The matrix Omega is defined in proposition 7.1 on p. 20. in his paper. 
% Its fourth power reflects the smoothness of the resulting density.
out = (diag(lambda([0:N],B).^(-1)));
end

%% Singular Value Decomposition functions 
function out = phi(k,xi,B)
out =   a1(k,B).*exp(rho(k).*xi./B) + a2(k,B).*exp(-rho(k).*xi./B) + ...
        a3(k,B).*cos(rho(k).*xi./B) + a4(k,B).*sin(rho(k).*xi./B);
end
function out = phi2(N,xi,B)
k = [0:N];
nr = length(xi);
nc = length(k);
out = zeros(nr,nc);
for l=1:nr
    out(l,:) =   a1(k,B).*exp(rho(k).*xi(l)./B) + ...
                 a2(k,B).*exp(-rho(k).*xi(l)./B) + ...
                 a3(k,B).*cos(rho(k).*xi(l)./B) + ...
                 a4(k,B).*sin(rho(k).*xi(l)./B);
end
end
function out = psi(k,xi,B)
out =   a1(k,B).*exp(rho(k).*xi./B) + a2(k,B).*exp(-rho(k).*xi./B) - ...
        a3(k,B).*cos(rho(k).*xi./B) - a4(k,B).*sin(rho(k).*xi./B);
end
function out = psi2(N,xi,B)
k = [0:N];
nr = length(xi);
nc = length(k);
out = zeros(nr,nc);
for l=1:nr
out(l,:) =   a1(k,B).*exp(rho(k).*xi(l)./B) + ...
             a2(k,B).*exp(-rho(k).*xi(l)./B) - ...
             a3(k,B).*cos(rho(k).*xi(l)./B) - ...
             a4(k,B).*sin(rho(k).*xi(l)./B);
end
end
function out = rho(k)
out=pi/2+k.*pi+(-1).^k.*beta(k);
end        
% singular value function 
function out = lambda(k,B)
out = (B./rho(k)).^2;
end
% coefficients in spectral decomposition
function out = a1(k,B)
out = 1./sqrt(B) .* (-1).^k ./ (exp(rho(k)) + (-1).^k);
end
function out = a2(k,B)
out = (-1).^k .* exp(rho(k)) .* a1(k,B);
end
function out = a3(k,B)
[r,c]=size(k);
out = -1./sqrt(B)*ones(r,c);
end
function out = a4(k,B)
out = 1./sqrt(B).*(1-(-1).^k .*exp(-rho(k)))./(1+(-1).^k.*exp(-rho(k)));
end

function out = beta(k)
% hardcoded values for solution u to fixed point equation:
% exp(pi/2+k*pi+(-1)^k*u)=(1+cos(u))/sin(u), p.4 in Monnier (2013) 
% %b(1) = beta(0)
b = [   0.304296874999999;0.0182979375620693;0.000775804281234741;
        3.35526888492169E-05;1.44989240095019E-06;6.26556264750743E-08;
        2.70759494442027E-09;1.17005786949584E-10;5.05627851300998E-12;
        2.18501606381235E-13;9.44231055865944E-15;4.08039236703066E-16;
        1.76329742232983E-17;7.61989906832813E-19;3.29285695516927E-20;
        1.4229725131498E-21;6.14922178748496E-23;2.65731967710182E-24;
        1.14833195326992E-25;4.96239231682844E-27;2.14444415972196E-28;
        9.26698346394484E-30;4.00462665962646E-31;1.7305560914602E-32;
        7.47841094872342E-34;3.23171439481034E-35;1.39655041709189E-36;
        6.03504155754466E-38;2.60797792586203E-39;1.12700944921924E-40;
        4.87024942210596E-42;2.10462560451071E-43;9.09491188491674E-45;
        3.93026778811002E-46;1.69842270950123E-47;7.33955001457214E-49;
        3.17170714422589E-50;1.37061893287199E-51;5.92298145359096E-53;
        2.55955236413318E-54;1.10608286655496E-55;4.77981745882654E-57;
        2.06554640981478E-58;8.92603537237651E-60;3.85728963001422E-61;
        1.66688598791128E-62;7.20326748366261E-64;3.11281412271079E-65;
        1.34516895069141E-66;5.81300210861437E-68;2.51202597988793E-69;
        1.0855448537135E-70;4.69106465800331E-72;2.02719284701028E-73;
        8.7602945995607E-75;3.78566654791975E-76;1.63593484775703E-77;
        7.06951547958296E-79;3.05501464099165E-80;1.32019152990442E-81;
        5.70506488658148E-83;2.46538207698245E-84;1.0653881956369E-85;
        4.60395984054396E-87;1.9895514423896E-88;8.59763134129952E-90;
        3.71537338044957E-91;1.60555841582145E-92;6.93824701490185E-94;
        2.99828839395849E-95;1.29567789587734E-96;5.59913186886186E-98;
        2.4196042692908E-99;1.0456058112381E-100;4.5184724062967E-102;
        1.9526089724282E-103;8.4379884535621E-105;3.6463854334288E-106;
        1.575746020784E-107;6.8094159746625E-109;2.9426154535309E-110;
        1.271619436906E-111;5.4951658409081E-113;2.3746764749486E-114;
        1.0261907509133E-115;4.4345723233009E-117;1.9163524591391E-118;
        8.2813098533818E-120;3.5786784712102E-121;1.5464871894719E-122;
        6.682977100181E-124;2.8879762616589E-125;1.2480077011904E-126;
        5.3931302791802E-128;2.3305829107036E-129;1.0071361941009E-130;
        4.3522301172363E-132;1.8807691655138E-133;8.1275404991538E-135;
        3.5122287081591E-136;1.5177716431807E-137;6.5588859731481E-139;
        2.8343516234503E-140;1.2248343938657E-141;5.2929893383167E-143;
        2.2873080863704E-144;9.8843544688477E-146;4.2714168610694E-147;
        1.8458465910475E-148;7.9766263712992E-150;3.4470128002996E-151;
        1.4895892940632E-152;6.437099000024E-154;2.7817227004285E-155;
        1.202091374088E-156;5.1947078385421E-158;2.2448367993894E-159;
        9.7008193964322E-161;4.1921041648904E-162;1.811572467348E-163;
        7.8285144532878E-165;3.3830078371113E-166;1.4619302415863E-167;
        6.3175733967248E-169;2.7300710039146E-170;1.1797706521743E-171;
        5.0982512533071E-173;2.2031541294862E-174;9.5206922474069E-176;
        4.1142641659416E-177;1.7779347538261E-178;7.683152713008E-180;
        3.3201913334816E-181;1.4347847690531E-182;6.2002671736177E-184;
        2.6793783885376E-185;1.1578643867918E-186;5.0035856971286E-188;
        2.1622454334165E-189;9.343909742688E-191;4.0378695187891E-192;
        1.7449216334592E-193;7.5404900843292E-195;3.2585412218713E-196;
        1.4081433401327E-197;6.0851391200938E-199;2.6296270456143E-200;
        1.1363648823966E-201;4.910677914114E-203;2.1220963395445E-204;
        9.1704097767052E-206;3.962893384877E-207;1.7125215077821E-208;
        7.4004764433878E-210;3.1980358437824E-211;1.3819965958997E-212;
        5.9721488046185E-214;2.5807995015207E-215;1.1152645859538E-216;
        4.8194952748242E-218;2.0826927439022E-219;9.000131388405E-221;
        3.8893094263271E-222;1.6807229829651E-223;7.2630627550915E-225;
        3.1386538548829E-226;1.3563354088323E-227;5.8612566458022E-229;
        2.5328784736287E-230;1.0945560461339E-231;4.7300060289896E-233;
        2.0440210748331E-234;8.833015873825E-236;3.8170929267781E-237;
        1.6495147726001E-238;7.1282063999879E-240;3.0803756760086E-241;
        1.3311523095098E-242;5.7524142252015E-244;2.4858450957909E-245;
        1.074235073086E-246;4.6421979697622E-248;2.006061281923E-249;
        8.6690451234472E-251;3.7462533308605E-252;1.6188589162288E-253;
        6.9957137077231E-255;3.0231243854192E-256;1.3063954638211E-257;
        5.645435401422E-259;2.4397634197098E-260;1.0541809751804E-261;
        4.5561391826726E-263;1.9688239427666E-264;8.510837770087E-266;
        3.6776866659057E-267;1.5885285269736E-268;6.8660345654539E-270;
        2.9691218129735E-271;1.2814558943987E-272;5.5320445505565E-274];
if size(k,2)>size(k,1)
    b=b';
end
out=b(k+1);
end

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