function [ x ] = gera_x_por_exclusao(n);
  xi = 0;
  xf = 2;
  yMax = 1;
  function f = f(x)
    f = (x/2);
  end
  x = nan(n,1);
  nOk = 0;
  while( nOk<n )
    xc = xi + (xf-xi)*rand;
    yv = yMax*rand;
    if yv<=f(xc)
      nOk = nOk+1;
      x(nOk) = xc;
    end
  end
end