function []=hw3_2_11(n)

% find the inverse of E in problem 2.10, try inputting values of n of 20 and 50 
E=zeros(n);
for i=1:n
    for j=1:n
        if (i==j)
            E(i,j)=i*(n-i+1);
        elseif (j>i)
            E(i,j)=E(i,j-1)-i;
        else
            E(i,j)=E(j,i);
        end
    end
end
E=1/(n+1)*E;
EI=inv(E);

% compare to the actual inverse, AI. norm(AI-EI) is like the "distance" between
% the two matrices, it should be small
AI=diag(-ones(1,n-1),-1)+diag(2*ones(1,n))+diag(-ones(1,n-1),1);
norm(AI-EI)