title: Maxima: Assign value to a variable, by addressing it in a matrix
body: <p>I had a complex problem which is solved. Now i would love to automate it. In doing so, I do address a position in a matrix. This positions does contain a variable. I want to assign a value to this variable, by its position in the matrix. Here is a simple example of what I want to do:</p>
  
  <pre><code>    (%i1) M:[a,b,c];
      (%o1) [a,b,c]
      (%i2) M[1];
      (%o2) a
      (%i3) ev(M[1]):3;
      (%o3) error: assignment: cannot assign to ev(M[1])
      (%i4) float(a);
      (%o4) a
  </code></pre>
  
  <p>I would love the variable "a" to be 3 now. But ev() is clearly not the right function for this.</p>
  
  <p>My question is: is what i want even possible? does anyone know how to do? I looked the whole day and I am really depressed now :-(</p>