title: Plotting solution of ODE in Maxima ("expression evalues to non-numeric value everywhere")
body: <p>I am solving for <code>w</code> in a 2nd order ODE using Maxima, it gives me some answer, but I am at loss as to how to plot the expression. The session looks like this:</p>
  
  <pre><code>eq: -E*(I0+I1*x)*'diff(w,x,2)=(f1/6)*x^3+(f0/2)*x^2+l*(f0/2+2*f1*l^2/3)*x;
  sol2: ode2(eq,w,x);
  solbc2: bc2(sol2,x=0,w=0,x=l,w=0);
  solNum: subst([E=1,I0=1,I1=1,f0=1,f1=1,l=1],solbc2);
  </code></pre>
  
  <p>When I try to plot <code>solNum</code> with</p>
  
  <pre><code>plot(solNum,[x,0,1]);
  </code></pre>
  
  <p>I am getting </p>
  
  <pre><code>plot2d: expression evaluates to non-numeric value everywhere in plotting   range.
  plot2d: nothing to plot.
  </code></pre>
  
  <p>I am Maxima beginner, I apologize if I overlooked something obvious. The tutorials I've crossed only show <code>plot2d</code> with an expression in it.</p>