[racket] "error: degrees->complex: 360.0"
Okay, then I'll go with this:
(define/contract (angle->proper-range α)
(-> real? (between/c 0 360))
(let loop ([θ (- α (* 360 (floor (/ α 360))))])
(cond [(negative? θ) (+ θ 360)]
[(>= θ 360) (- θ 360)]
[else θ])))
Can you point me to your random real number generator, btw?
Robby
On Tue, May 13, 2014 at 9:06 AM, Neil Toronto <neil.toronto at gmail.com> wrote:
> I can't get it to take more than on iteration, either. It's there in case I
> missed something. :)
>
> Neil ⊥
>
>
> On 05/13/2014 05:59 AM, Robby Findler wrote:
>>
>> Thanks, Neil!
>>
>> Why is the loop needed? I can't seem to get it to take more than one
>> iteration.
>>
>> Robby
>>
>> On Mon, May 12, 2014 at 11:24 PM, Neil Toronto <neil.toronto at gmail.com>
>> wrote:
>>>
>>> He went with exact rationals. Here's another option, which preserves
>>> inexactness:
>>>
>>> (define (angle->proper-range α)
>>> (let loop ([θ (- α (* 360 (floor (/ α 360))))])
>>> (cond [(negative? θ) (loop (+ θ 360))]
>>> [(>= θ 360) (loop (- θ 360))]
>>> [else θ])))
>>>
>>> Its accuracy drops off outside of about [-1e16,1e16].
>>>
>>> The fact that this is hard to get right might be good motivation for an
>>> `flmodulo` function.
>>>
>>> Neil ⊥
>>>
>>>
>>> On 05/12/2014 09:49 PM, Sean Kanaley wrote:
>>>>
>>>>
>>>> Interesting, my code has the same bug then. I called it modulo/real,
>>>> used for things like displaying the space ship's rotation to the user or
>>>> wrapping x coordinates to stay in the world. Apparently it's going to
>>>> fail at some point with vector ref out of range. What was your fix? I
>>>> was thinking to just clamp explicitly like mod/real = (max 0 (min
>>>> the-mod-minus-1 (old-modulo/real x)))
>>>>
>>>>
>>>> On Mon, May 12, 2014 at 11:12 PM, Robby Findler
>>>> <robby at eecs.northwestern.edu <mailto:robby at eecs.northwestern.edu>>
>>>> wrote:
>>>>
>>>> Right. Probably there is a better fix, but the essential problem,
>>>> as I
>>>> understand it, is that there are more floating points between 0 and
>>>> 1
>>>> than between any two other integers and the code made the
>>>> assumption
>>>> that that didn't happen....
>>>>
>>>> The basic desire is to turn a real number into a number in [0,360)
>>>> such that the result represents the same number in degrees but is
>>>> normalized somehow.
>>>>
>>>> Robby
>>>>
>>>> On Mon, May 12, 2014 at 10:06 PM, Danny Yoo <dyoo at hashcollision.org
>>>> <mailto:dyoo at hashcollision.org>> wrote:
>>>> > Wow. Floating point really is nasty. I see how it might have
>>>> happened now.
>>>> >
>>>> > ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
>>>> >> -0.0000000000000001
>>>> > -1e-16
>>>> >> (+ 360 -1e-16)
>>>> > 360.0
>>>> >>
>>>> > ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
>>>>
>>>>
>>>>
>>>>
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>>>>
>>>
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>
>