*sin, cos, and atan2 are "primitive" functions.
*
Well, once you have a routine for `sin`, then `cos` is the same thing, but `pi/2` sooner. And I'm fairly sure that's the way it's implemented in the libraries.
Using `atan2` to do an inverse `sin` or `cos` is a bit of a walk in the park, but essentially I guess you have to find the 'Y' value once you have the 'X', then submit both to `atan2`, and that will give you the angle you're looking for.
That's a nice brain exercise right after lunch.
Alex / talexb / Toronto
"Groklaw is the open-source mentality applied to legal research" ~ Linus Torvalds
| [reply] [d/l] [select] |

I suspect on most CPUs, it just uses the sin and cos opcodes of the native CPU. Implementing sin in terms of cos (or vice-versa) is just asking for problems, like the well-known results being a little off, since pi/2 cannot be exactly represented as a float (or as anything else in finite RAM).
| [reply] |

I know. But you can do away with either `sin` or `cos` as well - they are the same primitive, just shifted a quarter of a phase. That of course doesn't mean `tan` couldn't be present. After all, Perl gives us
`push`, `pop`, `shift` and `unshift`, when they can all be trivially implemented using `splice`. Perl is a rich language, and any minimal approach is, to quote `brian`, what I consider *exceptions to normal Perl thinking*. Normal Perl thinking is "programmer convenience". A minimalistic approach isn't programmer convenience. | [reply] Edit |

Howdy!
My sense is that push/pop/shift/unshift are much more frequently
used than the trig functions. On that basis, it makes Huffman sense
to provide the convenience of the push, etc. functions while declining
to provide a fuller set of trig functions.
| [reply] |

You can only explain that with "Huffman" if the save space of 'tan' actually allows you to do something else. Besides, for your reasoning to really work, you'd have to sacrifice one of sin or cos. The analogue would really be having 'splice', 'push' and 'unshift', but not 'pop' or 'shift'. ;-)
| [reply] Edit |

Comment onRe^2: Perl oddities