Comments on: Complex Issues

By: cjm

cjm — Thu, 08 Sep 2011 18:38:48 +0000

jamarier, I strongly disagree. You’re correct that in the mathematical sense, sqrt(x) has two answers, and asin(x) has an infinite number of answers.

But in a computer programming language, the range of the sqrt and asin functions should be defined such that there is only 1 correct answer for each possible input. Programming is hard enough as it is; any surprises that can be removed should be removed.

By: jamarier

jamarier — Thu, 08 Sep 2011 17:11:14 +0000

It’s a bad test because both answers are correct.

(sqrt 1)^3 can be 1 or -1. and both are ok answers.

Maybe a best test is something like ( asin(sin(asin x)) == asin x )

By: sorear

sorear — Thu, 01 Sep 2011 14:51:53 +0000

The Perl 6 specs already specify “principal” square root, which apparently means the same thing that POSIX and Common Lisp specify. Niecza has now been fixed to do that too.

By: salva

salva — Thu, 01 Sep 2011 09:09:18 +0000

follow C and POSIX (that AFAIK is similar to Common Lisp behavior):

http://pubs.opengroup.org/onlinepubs/009695399/functions/csqrt.html

By: cjm

cjm — Wed, 31 Aug 2011 19:26:48 +0000

1) Yes, there should be one “correct” answer for all Perl 6 implementations.

2) Let’s just follow Common Lisp. They’ve got the experience, and they’ve already written the definitions. Just make sure we get the current definitions. (I’m not a Lisp expert, so I’m not sure if the link you mention is up-to-date.)

Here’s another link to look at:
http://www.ai.mit.edu/projects/iiip/doc/CommonLISP/HyperSpec/Body/fun_asincm_acoscm_atan.html

By: colomon

colomon — Wed, 31 Aug 2011 16:00:42 +0000

http://www.ida.liu.se/imported/cltl/clm/node129.html looks to have some interesting info…