New package for drawing direction fields with gnuplot

Adam Majewski <adammaj1 at o2.pl> writes:
> soln_at draw field lines, so how can I draw equipotential lines ?

With the attached patch to drawdf.mac, does the following command do
what you want?

drawdf(x*x+y*y, [x,-2,2], [y,-2,2],
  field_color=gray, proportional_axes='xy, aspect_ratio=1,
  color=red, solns_at(makelist([k/2,-k/2],k,-3,3)),
  color=green, equipots_at(makelist([k/2,k/2],k,-3,3)))$

Note that equipots_at uses the same numerical integrator as solns_at, so
you may sometimes have to mess around with options such as duration and
tstep to get good results.

    Mark


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