[PD] more about float limitation (was: weird float/add limitation)

[Cyrille Henry]

Le 31/01/2015 07:46, Alexandre Torres Porres a écrit :
> So, cant we raise the bit resolution of pd to more than what's there? how?
by replacing float by double.
katja made a lot's of work around this
http://www.katjaas.nl/doubleprecision/doubleprecision.html
there are lot's of mail in this list to read, search the archive for pd double.


but this ill not solve the precision problem, just move it...

cheers
c

>
> Martin, about the pi in lua, i never got to see it, but supercollider prints the value of pi as
>
> 3.1415926535898
>
> so thats more than 24 bit float, but what is it?
>
> cheers
>
> 2015-01-29 15:47 GMT-02:00 Martin Peach <chakekatzil at gmail.com <mailto:chakekatzil at gmail.com>>:
>
>     Here's a patch using pdlua that shows the value of pi in various ways. I get 48 decimal places in a symbol.
>
>     Martin
>
>     On Thu, Jan 29, 2015 at 12:36 PM, Alexandre Torres Porres <porres at gmail.com <mailto:porres at gmail.com>> wrote:
>
>         >more that 7 digit but less than 8 digits
>         ...
>         > so, 4/3 =! 1.33333
>         > but 4/3 == 1.33333333 (8 "3")
>
>         I don't get it. More than 7 decimal digits but less than 8 decimal digits? How does that work? In practice, is it 7 or 8?
>
>         In the example we see that 4/3 == 1.33333333 (8 "3") - so it's 8 decimal digits...
>
>         I have a work around using expr. Just put the number in parenthesis.
>
>         Try [expr 4./3 == (1.33333333)] (8 "3")
>
>         but the thing is that this is also true - [expr 4./3 == (1.3333333)] - also equal to 7 "3"
>
>         cheers
>
>         2015-01-29 14:58 GMT-02:00 Cyrille Henry <ch at chnry.net <mailto:ch at chnry.net>>:
>
>             hello,
>
>             ok, claude was faster to answer, but since i already write my mail, i send it anyway...
>
>
>             pd internal resolution is float32.
>             (i.e, 23 bit, so a bit less than 17 millions, i.e more that 7 digit but less than 8 digits)
>             pd graphical representation is 6 digits
>
>             so, 4/3 =! 1.33333 but 4/3 == 1.33333333 (8 "3")
>             even if both are represented with the same number of 3...
>             this is a generic problem of computer float.
>
>             the only odd thing concerning pd is that number are also saved with 6 digit.
>             (so precision can be lost when a patch is saved)
>
>             try the attachment patch.
>             then save the patch, and open it back, and see that precision is lost.
>             (I have to modifies the patch as text file to have this behaviors, but you can also have the save precision when creating an object... until you save/load the patch)
>
>             you can also have a look on the top right of the patch: a weird effect of float precision...
>
>             cheers
>             c
>
>             Le 29/01/2015 17:17, Alexandre Torres Porres a écrit :
>
>                 Well, thanks everyone.
>
>                 And now for some related issues.
>
>                 Pd can only represent up to 6 significant digits, so they say. For example, in a message, you can have a number with up to 5 decimal places, like: -5.29314e+12
>
>                 but it does have a better internal resolution, if you compare 4 / 3 to 1.33333 you'll see 4 / 3 is higher ( try [expr 4./3 > 1.33333] and check).
>
>                 So, what's this internal resolution? And why can't you have the same resolution in a message?
>
>                 thanks
>
>                 2015-01-28 16:06 GMT-02:00 Martin Peach <chakekatzil at gmail.com <mailto:chakekatzil at gmail.com> <mailto:chakekatzil at gmail.com <mailto:chakekatzil at gmail.com>>__>:
>
>                      On Wed, Jan 28, 2015 at 12:00 PM, Cyrille Henry <ch at chnry.net <mailto:ch at chnry.net> <mailto:ch at chnry.net <mailto:ch at chnry.net>>> wrote:
>
>
>
>                          Le 28/01/2015 17:47, Alexandre Torres Porres a écrit :
>
>                                > it's a limitation of 32 bit float
>
>                              I thought so, but same happens when I use the new Pd Vanilla 64 bits...
>
>                          this mean that it's compiled for 64 bit CPU, not that float are store on 64 bits
>
>                      Also last time I checked, Pd saves floats by first printing them to 6 digit precision, so they have even less range than a 'float' type.
>                      You could use an object made with pdlua to manipulate large floating-point numbers, as there is no(?) limit to the size of a float in lua.
>
>                      Martin
>
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