[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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>
>