New submission from Mark Dickinson: IEEE 754, the C99 standard, the Decimal IBM standard and Java all support/specify a 'remainder-near' operation. Apart from being standard, this has a number of useful applications:
1. Argument reduction in numerical algorithms: it's common to want to reduce to a range [-modulus/2, modulus/2] rather than [0, modulus). 2. Particular case of the above: reduction of angles to lie in the range [-pi, pi] 3. Rounding a float x to the nearest multiple of y. This is a much-asked StackOverflow question, and the standard answer of y * round(x / y) risks introducing floating-point error and so can give incorrect results in corner cases. With a remainder operation, it's trivial to do this correctly: x - remainder(x, y) gives the closest representable float to the closest integer multiple of y to x. remainder(x, y) has some nice properties: it's *always* exactly representable (unlike x % y), it satisfies the symmetry remainder(-x, y) == -remainder(x, y), and it's periodic with period 2*y. I have a patch, and will make a PR shortly. ---------- components: Extension Modules messages: 290985 nosy: mark.dickinson priority: normal severity: normal stage: patch review status: open title: Add math.remainder operation type: enhancement versions: Python 3.7 _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue29962> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
