s_tcopulasimul.m

来自「经济学专业代码」· M 代码 · 共 58 行

% this script simulates the copula of a bi-variate t distribution
% see "Risk and Asset Allocation"-Springer (2005), by A. Meucci

clc; clear; close all
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% input parameters
Mu=[10  -1]';     
r=-.3;            
sigma=[20 10]';    
nu=1;

NumSimul=20000;

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C=[1 r;r 1];
Std_X=mvtrnd(C,nu,NumSimul);  % standardized bi-variate t simulation
X_1=Mu(1)+sigma(1)*Std_X(:,1);
X_2=Mu(2)+sigma(2)*Std_X(:,2);
X=[X_1 X_2];                  % bi-variate t simulation

U_1=tcdf((X(:,1)-Mu(1))/sigma(1),nu); % grade 1 simulation
U_2=tcdf((X(:,2)-Mu(2))/sigma(2),nu); % grade 2 simulation
Copula = [U_1 U_2];			      % copula

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% plots
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

figure 
% marginals
NumBins=round(10*log(NumSimul));

subplot('Position',[.05 .3 .2 .6]) 
[n,D]=hist(Copula(:,2),NumBins);
barh(D,n,1);
[y_lim]=get(gca,'ylim')
set(gca,'xtick',[])
grid on

subplot('Position',[.3 .05 .6 .2]) 
[n,D]=hist(Copula(:,1),NumBins);
bar(D,n,1);
[x_lim]=get(gca,'xlim')
set(gca,'ytick',[])
grid on

% scatter plot
subplot('Position',[.3 .3 .6 .6]) 
h=plot(Copula(:,1),Copula(:,2),'.');
set(gca,'xlim',x_lim,'ylim',y_lim)
grid on
xlabel('grade 1');
ylabel('grade 2');

% 3-d histogram (~rescaled pdf)
NumBins3d=round(sqrt(NumSimul)/5);
figure
hist3(Copula(:,[1 2]),[NumBins3d NumBins3d]);title('pdf copula')