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

[Alexandre Torres Porres]

i got extended 0.42-5, it doesn't happen

2015-01-29 16:22 GMT-02:00 Martin Peach <chakekatzil at gmail.com>:

> 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
>>>>>>
>>>>>>     _______________________________________________
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>>>>>>
>>>>>>
>>>>>>
>>>>
>>>
>>
>
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