N = 100;
 g = 0.4;
 A = exp(-g)*diag(ones(N-1,1),-1) + ...
       diag(3*rand(N,1)-1.5) + ...
       exp(g)*diag(ones(N-1,1),1);
 opts.npts = 20;
 opts.ax = [-4 4 -1.5 1.5];
 opts.levels = [-11:-1]; 
 eigtool(A, opts)