New package for drawing direction fields with gnuplot

Dnia Sat, 20 Nov 2010 08:07:47 -0500, Mark H Weaver napisa?(a):

> Robert Dodier wrote:
>> Evaluating f(x, y) with symbolic arguments triggers the error. Try
>> postponing evaluation of f, e.g. drawdf(f, ...) (not sure if that
>> works) or drawdf('(f(x, y)), ...).
> 
> Adam Majewski <adammaj1 at o2.pl> wrote:
>> (%i10) drawdf('f(x,y), [x,-2,2], [y,-2,2]); draw: graphical 2d object
>> errexp1 is not recognized
> 
> '(f(x,y)) is not the same as 'f(x,y).  The first quotes the entire
> subexpression.  The second uses the noun form of f.
> 
> Passing '(f(x,y)) to drawdf works.  Passing f or 'f(x,y) fails.
> 
>     Mark

You are right. It works now. 

I have tried :

drawdf('(f(x,y)), [x,-2,2], [y,-2,2]);
drawdf('(f(x,y)), [x,-2,2], [y,-2,2],soln_at(1,1));

drawdf('(f(x,y)), [x,-2,2], [y,-2,2],equipots_at(1,1));

I was expecting that field lines will be straight lines towards (0,0)
and equipotential lines will be concentric circles
like on the left image :
http://commons.wikimedia.org/w/index.php?title=File:Jung50e.png
Maybe I should mess around with options such as duration and
tstep to get good results.
Here can I find description of options ?

Adam