% Script TrySparse
% use the gallery to produce Poisson matrices of different sizes and show
% that they are sparse as n increases.  Show percentage of nonzero entries
% for increasing n

disp(' ')
disp(' Sparsity of Poisson matrix for increasing size ')
disp(' n       All   Nonzero Fraction')
for n = 2:2:30
    A = gallery('poisson',n);  % result is n^2 by n^2
    all = n^2*n^2;
    nonzero = sum(sum(full(A)~=0)); 
    frac = nonzero/all;
    disp(sprintf(' %3.0f   %6.0f   %6.0f  %7.5f',n^2,all,nonzero,frac))
end