s_normal.m

来自「经济学专业代码」· M 代码 · 共 66 行

% this script simulates a bivariate normal distribution
% it shows its pdf as proxied by the 3-D histogram
% it shows the distribution of a generic linear combination (portfolio) of the two variables
% it computes the summary statistics of the market
% see "Risk and Asset Allocation"-Springer (2005), by A. Meucci

clc; clear; close all
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% input parameters

Mu=[0.04 0.05]';
s=[.25 .30]';
r=-.8;

NumSimulations=100000;
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Sigma=[s(1)^2     r*s(1)*s(2)
    r*s(1)*s(2)    s(2)^2];

% generate sample
X = mvnrnd(Mu,Sigma,NumSimulations);

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

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

subplot('Position',[.05 .3 .2 .6]) 
[n,D]=hist(X(:,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(X(:,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(X(:,1),X(:,2),'.');
set(gca,'xlim',x_lim,'ylim',y_lim)
grid on

% 3-d histogram (~rescaled pdf)
NumBins3d=round(sqrt(NumSimulations)/5);
figure
hist3(X,[NumBins3d NumBins3d]);

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% compute summary statistics (analytical and sample-based)
Expected_Value=Mu'
Covariance=Sigma;
Standard_Deviation=sqrt(diag(Covariance))'
Correlation=r

Sample_Mean=mean(X)
Sample_Covariance=cov(X);
Sample_Standard_Deviation=sqrt(diag(Sample_Covariance))'
Sample_Correlation=Sample_Covariance(1,2)/(sqrt(Sample_Covariance(1,1)*Sample_Covariance(2,2)))