1st try!

n=size(a,1);
a=a-diag(diag(a));
for i=1:n
   for j=1:n
      d(i,j)=norm(b(i,:)-b(j,:))/a(i,j);
   end
end

Z=zeros(1,n);
p=Z;
m=Z;
D=Z;
p(1)=-1;
k=1;

while ~all(m)
   l=Z
   for j=k
      q=~~a(j,:)&~p
      if any(q)
         p(q)=j
         D(q)=D(q)+d(j,q)+D(j)
         l=l|q & ~m
      end
   end
   m(k)=1
   k=find(l)
end
L=0;
while L~=D
   L=D;
   for i=2:n
      q=~~q(i,:);
      [y v] = min(d(i,q)+D(q));
      if y<D(i)
         p(i)=v;
         D(i)=y;
      end
   end
end

[y v]=max(D);

c=[];
while v>0
   c=[v,c];
   v=p(v);
end