Re: [Bug-apl] Floating-point random number function

[Christian Robert]

On 2017-06-30 00:19, Elias Mårtenson wrote:
> Thanks. I'll stick with this for now then.
>
> How would (res+V×0) wrap around, by the way?

Bad first reading, (res+V×0) does nothing, it add 0 to "res". How is it usefull 
?

Xtian.


> On 30 June 2017 at 12:17, Christian Robert <address@hidden 
> <mailto:address@hidden>> wrote:
>
>     I think this is the best you can get, about 62 bits of randomness.
>
>            (64⍴2) ⊤⎕syl[20;2] ⍝ the largest 64 bits integer supported by gnu-apl
>     0 1 1 1 1 1 1 1 1 0 1 0 1 1 0 0 1 1 1 1 0 1 1 1 0 1 0 0 0 0 0 1 1 0 0 1 1 1 
> 0 1 1 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
>
>     so, it's a bit less than 63 bits, say 62 bits for safety is Ok.
>
>     Note that (res+V×0) may wrap around.
>
>     Xtian.
>
>     On 2017-06-29 23:23, Elias Mårtenson wrote:
>
>         I had a need to have a function that does the same as monadic ?, but 
> with the difference that the resulting numbers not be integers, but floating 
> point.
>
>         Now, here's my attempt at creating such a function, I'd like to know if 
> this is the best way to achieve what I need:
>
>         ∇ r←*hrRand* V ;res
>             ⍝⍝ Like monadic ?, but returns floating point numbers
>             res ← ⎕SYL[19+⎕IO;1+⎕IO]
>             r ← V × res÷⍨ ?res+V×0
>         ∇
>
>         Example:
>
>         *      hrRand 3 2 ⍴ 10 100 5 (3 4 (2 2⍴5)) 1000*
>         
> ┏→━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
>         ↓ 4.138685128 <tel:4.138685128>                                         
>           54.55782413 ┃
>         ┃  0.4543486424           
> ┏→━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓┃
>         ┃                         ┃2.024528001 <tel:2.024528001> 2.772781338 
> ┏→━━━━━━━━━━━━━━━━━━━━━━┓┃┃
>         ┃                         ┃                        ↓3.185551114 
> <tel:3.185551114> 3.13571477 ┃┃┃
>         ┃                         ┃                        ┃1.204617876 4 
> <tel:204617876%204>.396324338┃┃┃
>         ┃                         ┃                        
> ┗━━━━━━━━━━━━━━━━━━━━━━━┛┃┃
>         ┃                         
> ┗∊━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┛┃
>         ┃634.0902523                                                      
> 9.353801479┃
>         
> ┗∊∊━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┛
>
>         Regards,
>         Elias