title: How to simulate and draw electric fields in Matlab with contourf?
body: <p>I'd like to know how to draw a graph with 2 electric charges Q and -Q and their total E, for a specific point (eg (4,5)), with contour f..
  My M-file actually scans the area (from -3x to 3x) and calculates E for every spot, stores it in a table, but after this, I don't know how to use contourf to draw it..</p>
  
  <pre><code>syms i
  syms j
  syms d
  d=input('dwse thn timi tou d,ths apostashs')
  j=0
  i=0
  for j=-d:d/1000:d
  
      j=j+1
  
  for i=-d:d/1000:d
  
      i=i+1
      z=(i,j)
  
  end, end
  </code></pre>