Tests

[floydes]

http://oomph-lib.maths.man.ac.uk/doc/poisson/one_d_poisson/html/
http://ammar-hakim.org/sj/je/je11/je11-fem-poisson.html
http://www.ie.itcr.ac.cr/acotoc/Maestria_en_Computacion/Sistemas_de_Comunicacion_II/Material/Biblio2/chapt07.pdf