title: assigning in system of differential equations
body: <p>when i solve numerically a system of two differential equations:</p>
  
  <pre><code>s1:=diff(n[Di](t), t)=...;
  s2:=diff(n[T](t), t)=...;
  ics:={...};   #initial condition.
  sys := {s1, s2, ics}: 
  sol:=dsolve(sys,numeric);
  </code></pre>
  
  <p>with respect to "t",then the solution (for example)for "t=4" is of the form, sol(4):</p>
  
  <pre><code>[t=4, n1(t)=const1, n2(t)=const2].
  </code></pre>
  
  <p>now, how is possible to use values of n1(t) and n2(t) for all "t"'s in another equation, namely "p", which involved n1(t) or n2(t)(like: {p=a+n1(t)*n2(t)+f(t)},where "a" and "f(t)" are defined), and to plot "p" for an interval of "t"?</p>