function plotx(A, t1=0, t2=NaN, m='r-')
  if (strcmp(typeinfo(t1),'string') || strcmp(typeinfo(t1),'sq_string'))
    m = t1;
    t1 = 0;
  endif
  
  if (strcmp(typeinfo(t2),'string') || strcmp(typeinfo(t2),'sq_string'))
    m = t2;
    t2 = NaN;
  endif

  n1 = point(A, t1);
  n2 = point(A, t2);

  plot(A(n1:n2,1), A(n1:n2,2), m)  

endfunction
