[D,x] = cheb(40);    % cheb.m from Trefethen's "Spectral Methods in MATLAB"
  A = D^2/1600 + D/40;
  A = A(2:end-1,2:end-1); 
  opts.npts=50;
  opts.ax = [-3.75 0.25 -1.25 1.25];
  opts.levels = -10:-1;
  eigtool(A,opts)