I found a java applet for visualizing the magnetic field of a specified
configuration of magnets on Paul Falstad's web site:
http://www.falstad.com/emwave2/directions.html
To use this applet, I first pressed "clear all." Then I selected "Mouse = Add Magnet (Down)" and painted in the location of one magnet and similarly for another magnet (Up) and for a feromagnetic (iron) plate below.
The figure below shows orientation of the B lines. Higher intensities are white and lower are green.
