function [A,kA,tc] =Aalfa(n,alfa);
v = ones(n,1);
A=diag(alfa*v)-diag(v(1:n-1),1)-diag(v(1:n-1),-1);
% A = spdiags([v alfa*v v],-1:1,n,n);
tic; kA(1) = cond(A,1); tc(1) = toc;
tic; kA(2) = cond(A,2); tc(2) = toc;
tic; kA(3) = cond(A,inf); tc(3) = toc;