[racket] "error: degrees->complex: 360.0"

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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