Exact fundamental solutions are known for operators of various types. We indicate a general approach that gives various old and new fundamental solutions for operators with double characteristics. The solutions allow one to read off detailed behavior, such as the presence or absence of analytic hypoellipticity. Recent results for operators with multiple characteristics are also described.
@incollection{JEDP_1998____A1_0, author = {Beals, Richard}, title = {Solutions fondamentales exactes}, booktitle = {}, series = {Journ\'ees \'equations aux d\'eriv\'ees partielles}, eid = {1}, pages = {1--9}, publisher = {Universit\'e de Nantes}, year = {1998}, zbl = {01808711}, language = {fr}, url = {http://archive.numdam.org/item/JEDP_1998____A1_0/} }
Beals, Richard. Solutions fondamentales exactes. Journées équations aux dérivées partielles (1998), article no. 1, 9 p. http://archive.numdam.org/item/JEDP_1998____A1_0/
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