n=1000;
b=[1:n]';
a1=sparse(1:n,1:n,1,n,n);
a2=sparse(2:n,1:n-1,1,n,n);
a=a1+a2+a2';
tic;
x=a\b;
t1=toc;
aa=full(a);
tic;
xx=aa\b;
t2=toc;
y=sum(x);
yy=sum(xx);
tic;
eig(a);
t3=toc
tic;
eig(aa);
t4=toc