title: Simulink model error
body: <p>I've had to create the Simulink Diagram after this picture:</p>
  
  <p><img src="https://i.stack.imgur.com/gCRbB.png" alt="Diagram"></p>
  
  <p>My answer is this one:</p>
  
  <p><img src="https://i.stack.imgur.com/wVrOT.png" alt="Simulink image"></p>
  
  <p>I've gave some values to <code>a</code>, <code>b</code> and <code>c</code> (like 3, 4 and 5), but when I try to run it, it gives me the following warning:</p>
  
  <blockquote>
    <p>Warning: The model 'ex2_2' does not have continuous states, hence Simulink is using the
    solver 'VariableStepDiscrete' instead of solver 'ode45'. You can disable this diagnostic by
    explicitly specifying a discrete solver in the solver tab of the Configuration Parameters
    dialog, or by setting the 'Automatic solver parameter selection' diagnostic to 'none' in the
    Diagnostics tab of the Configuration Parameters dialog </p>
    
    <p>Warning: 'ex2_2/Unit Delay' is discrete, yet is inheriting a continuous sample time; consider
    replacing unit delay with a memory block. When a unit delay block inherits continuous sample
    time, its behavior is the same as the memory block. Unit delay block's time delay will not be
    fixed and could change with each time step. This might be unexpected behavior. Normally, a
    unit delay block uses discrete sample time. You can disable this diagnostic by setting the
    'Discrete used as continuous' diagnostic to 'none' in the Sample Time group on the
    Diagnostics pane of the Configuration Parameters dialog box. "</p>
  </blockquote>
  
  <p>and the output (<kbd>scope</kbd>) it's just a step signal...</p>
  
  <p>I don't know where I'm wrong here.</p>