Dear friends,

To convert a PSTricks-code picture into a graphic file ".pdf", as doing an exercise, run
the file "convert.tex" by the following steps:

  1) latex convert.tex (you automatically get the output file "convert-fig1.tex", then put the definitions in the preamble
     of the convert.tex file in that of the convert-fig1.tex file).
  2) latex convert-fig1.tex
  3) dvips convert-fig1.dvi
  4) call the file "convert-fig1.ps" by the Ghostview progam to convert this file into its
   eps version (you can rename the result, say "fig1.eps").
  5) use the eps2pdf program to convert the file "fig1.eps" into the file "fig1.pdf".

The file "test.pdf" contains the vector field of the differential equation y'=2xy/(1+y^2).
Check your file "fig1.pdf" to see this vector field!

Enjoy!
