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

[Alexandre Torres Porres]

and how does one use [lpi] in a mac?

2015-01-29 15:47 GMT-02:00 Martin Peach <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> 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>:
>>
>> 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>>:
>>>>
>>>>     On Wed, Jan 28, 2015 at 12:00 PM, Cyrille Henry <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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>>>>
>>>>
>>>>
>>
>
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