Francesco Biscani added the comment: The best reference I could find so far is in the C99 standard:
http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf Annex G is titled "IEC 60559-compatible complex arithmetic". In G.3.1 it is written: """ A complex or imaginary value with at least one infinite part is regarded as an infinity (even if its other part is a NaN). """ Later on, in G.5.1.4, it is stated: """ The * and / operators satisfy the following infinity properties for all real, imaginary, and complex operands: - if one operand is an infinity and the other operand is a nonzero finite number or an infinity, then the result of the * operator is an infinity; - if the first operand is an infinity and the second operand is a finite number, then the result of the / operator is an infinity; - if the first operand is a finite number and the second operand is an infinity, then the result of the / operator is a zero; """ So to recap, according to these definitions: - inf + nanj is a complex infinity, - (inf + nanj) * (2 + 0j) should give a complex infinity (i.e., a complex number in which at least one component is inf). I am not saying that these rules are necessarily "mathematically correct". I am aware that floating point is always a quagmire to get into, and the situation here is even more complex (eh!) than usual. But it seems to me that Python, or CPython at least, follows a pattern of copying (or relying on) the behaviour of C for floating-point operations, and it seems like in the case of complex numbers this "rule" is broken. It certainly caught me by surprise anyway :) ---------- _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue25453> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
