n=input('n=')
for i=1:n
   for j=1:n
      a(i,j)=1/(i+j);
   end
end
b=zeros(n,1);
for i=1:n
   b(i)=0;
   for j=1:n
      b(i)=b(i)+a(i,j);
   end
end

x=a\b;
xe=ones(n,1); er=norm(x-xe,2)


cond(a,2)

x2 = pinv(a)*b; er=norm(x2-xe,2)