Code covered by the BSD License

Risk and Asset Allocation

Attilio Meucci (view profile)

16 Nov 2005 (Updated )

Software for quantitative portfolio and risk management

S_DisplayWishartPDF.m
```% this script displays the pdfs of the 1x1 Wishart distribution,
% i.e. the gamma distribution
% see "Risk and Asset Allocation"-Springer (2005), by A. Meucci
% formula (2.230)

clc; clear; close all
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% input parameters
nu=10;
sigma_square=2;
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

% generate sample to define grid
NumSimul=10000;
a=nu/2;
b=2*sigma_square;

% generate sample using matlab functions
W=gamrnd(a,b,NumSimul,1);

Percentile=.05;
Max=prctile(W,100*(1-Percentile));
Min=prctile(W,100*Percentile);
Step=(Max-Min)/50;
Grid=[Min : Step : Max];

% compute pdf on grid (and double check with gamma distribution)
for j=1:length(Grid)
w=Grid(j);
f_Wishart(j)=WishartPDF(w,nu,sigma_square);
f_Gamma(j)=gampdf(w,a,b);
end

% display pdf
figure
plot(Grid,f_Wishart,'.')
hold on
plot(Grid,f_Gamma,'r')
legend('Wishart','gamma')
grid on```