Le 13/09/2019 à 15:04, Samuel Gougeon a écrit :
Le 04/09/2019 à 09:11, Federico Miyara a écrit :
Dear all,
I need to create a boolean vector, such as [%t, %t, %t, %t] but with
a number of components given by a variable n. I couldn't find a
function similar to ones(1,n).
However I've found a workaround:
a = ones(1,n) & %t
It shouldn't work because ones(1,n) is not boolean, but it does.
Questions:
1) Why does it work?
2) Is there some native function to create bolean matrices
3) If not, are there any plans to introduce functions such as
true(m,n) or false(m,n)?
I hope no. These are typical -- IMO fake -- functions that i would not
expect in Scilab (and in any other language). There are many trivial
and fast ways to create a boolean array of given dimensions.
To me, the only need is to document these trivial ways in the help
pages of %F and %T.
Replacing a few lines of documentation with a lot of trivial
duplicated codes, separate pages, separate tests always look a very
bad idea to me.
But i can understand that, for some habit reason, former octavers
would appreciate their usual functions.
This is why i don't clearly understand why this sub-community does not
build /and maintain/ a "Matlabic" ATOMS package gathering this kind of
"aliases", or do not invest time to contribute to the m2sci converter
improvement.
Even when repmat() will be fastened by a factor 7 through its upgrade
pending for 7 months now
<https://antispam.utc.fr/proxy/2/c3RlcGhhbmUubW90dGVsZXRAdXRjLmZy/codereview.scilab.org/#/c/19782>,
it won't be the optimal way, noticeably due to its overhead.
I am neither very convinced by the ones(m,n,.,"boolean") and
zeros(m,n,.. "boolean") proposal, for the same reason initially
exposed by Alain. But why not.
In the same commit, Stéphane proposes to allow using the *"logical"*
keyword as an equivalent of the "boolean" one. On this side, i
definitively disagree with this. Indeed,
1. it would be useless, adding strictly no value to scilab
2. it would introduce a confusion for everyone, including for former
octavers, since in Octave an array of logical type is made of 0
and 1, not of %F and %T. While in Scilab we can also have arrays
of 0 and 1.
OK Samuel, I can forget this one. However, "double" should be kept as an
equivalent of "constant", even if not the name of a scilab type returned
by typeof(). We already have the macro "double()" (instead of
"constant()") and the keyword "double" used everywhere in the API.
1.
About trivial ways, a preliminary note -- and answer to Federico :
2) How much memory does it take a boolean scalar? Does a boolean
vector eploit the fact that a byte could theoretically host up to 8
boolean components?
4 bytes / boolean. This big memory waste is reported since a while:
http://bugzilla.scilab.org/12789
I think it was stored as 4 bytes for historical reasons (in Visual
Studio up to version 4.2 C++ int was 4 bytes)
This means that, using an array of decimal numbers to create a boolean
array uses an intermediate memory "only" ~twice bigger than the final
result.
About some trivial efficient ways:
* Array of %F :
o zeros(m,n,..)==1
as Christophe does, the way i use when, for 99,5% of cases, a
factor 2 in intermediate memory is not critical
o a(m,n,..) = %f;
or safer:
clear a, a(m,n,..) = %f;
* Array of %T :
o zeros(m,n,..)==0
o a(m,n,..) = %f; ~a
* Random boolean array :
o rand(m,n,..) < 0.5
Personnaly, i don't need any option for getting all this. But
documenting it would be useful.
In the same way, we can use
* clear c, c =(5,4,7) = %i*0 // to initiate an array of 0+0i
complex-encoded array
* clear p, p(5,4,7) = %z*0 // to initiate an array of 0z polynomials
* etc
.. still without any specific functions or option.
Best regards
Samuel
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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
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