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

[Martin Peach]

If you have pd-extended it will open lpi with the built-in pdlua loader.
I placed lpi-test and lpi.pd_lua in a directory and started pd-extended
from there.
You can also right-click on the lpi object to open it in an editor.

Martin

On Thu, Jan 29, 2015 at 1:05 PM, Alexandre Torres Porres <porres at gmail.com>
wrote:

> 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
>>>>>
>>>>>     _______________________________________________
>>>>>     Pd-list at lists.iem.at <mailto:Pd-list at lists.iem.at> mailing list
>>>>>     UNSUBSCRIBE and account-management -> http://lists.puredata.info/
>>>>> listinfo/pd-list
>>>>>
>>>>>
>>>>>
>>>
>>
>
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