[Scilab-users] display of complex/not real numbers, again

[Stéphane Mottelet]

Le 13/09/2019 à 17:20, Stéphane Mottelet a écrit :
>
> Le 13/09/2019 à 17:13, Samuel Gougeon a écrit :
>> Le 13/09/2019 à 16:59, Stéphane Mottelet a écrit :
>>>
>>>
>>> Le 13/09/2019 à 16:52, Samuel Gougeon a écrit :
>>>> Le 13/09/2019 à 14:22, Stéphane Mottelet a écrit :
>>>>>
>>>>> However, as I already said it elsewhere, some glitches such as the 
>>>>> following  one do occur (see the display of whole x)
>>>>>
>>>>> --> x=1:0.1:2
>>>>>  x  =
>>>>>    1.   1.1   1.2   1.3   1.4   1.5   1.6   1.7000000 1.8 1.9   2.
>>>>>
>>>>
>>>> I agree with Christophe. This output is OK for me. Aestheticism 
>>>> must be encouraged provided that it does not truncate or downgrade 
>>>> the information.
>>>>
>>>> About padding every number: Not OK. This would kill one of the 
>>>> assets of the "v" format: its compacity.
>>>>
>>>> About the fact that 1.7 can't be exactly encoded: It is very 
>>>> surprising for a so limited decimal number. But OK. I am also quite 
>>>> surprised that, in this series, only 1.7 can't be exactly encoded.
>>>>
>>> bitstring allows to see that only 1, 1.5 and 2 are exactly encoded
>>>
>>
>> So, question: Why 1.1 1.2 1.3 1.4 1.6 1.8 and 1.9 are displayed 
>> without trailing 0, while 1.7 is?
The actual algorithm in addDoubleValue() in tostring_common.cpp is quite 
simple. The decimal representation of the number x to display is first 
determined up to the current format settings. The obtained string is 
then converted back to a double y with atof(). If x and y differ, then 
trailing zeros can eventually be displayed if the settings allow it.
>> The argument/explanation according to which 1.7 can't be exactly 
>> encoded does not tell all...
>
> By using format(24) in current Scilab version you will have the 
> explanation :
>
> --> (1:0.1:2)'
>  ans  =
>
>    1.
>    1.100000000000000088818
>    1.199999999999999955591
>    1.300000000000000044409
>    1.399999999999999911182
>    1.5
>    1.600000000000000088818
>    1.700000000000000177636
>    1.8
>    1.9
>    2.
>
> You have (1.700000000000000177636-1.7) >= %eps but for the others the 
> difference is lower
>
>
>>
>>
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>>
>
-- 
Stéphane Mottelet
Ingénieur de recherche
EA 4297 Transformations Intégrées de la Matière Renouvelable
Département Génie des Procédés Industriels
Sorbonne Universités - Université de Technologie de Compiègne
CS 60319, 60203 Compiègne cedex
Tel : +33(0)344234688
http://www.utc.fr/~mottelet