[Scilab-Dev] Question about sparse(ij,v,mn) internals

[Samuel Gougeon]

Le 12/05/2015 10:14, Samuel Gougeon a écrit :
> Le 12/05/2015 08:34, Stéphane Mottelet a écrit :
>> .../...
>>
>> Le 11/05/2015 21:16, Samuel Gougeon a écrit :
>>> .../...
>>> I may miss something: how do you specify the position of terms to be 
>>> set with the v content? Is A already set, and you just want to 
>>> replace its nz terms? Is .nzval the "list" of positions (in such a 
>>> way that we could read A(nzval) .= v , and then what is the 
>>> equivalent with the spset(A,v)
>> no, nzval is really the field name such that A.nzval has the value v 
>> sucht that [ij,v]=spget(A). In Julia, the fields of a sparse matrix are
>>
>> julia> A.
>> colptr m       n       nzval   rowval
>>
>> colptr and rowval give the indices for the classical column 
>> compressed format. The nzval field is of read-write type so that the 
>> non zero elements can be updated by "A.nzval=v" if v has the correct 
>> size and corresponds to correctly ordered (column-wise) unique 
>> (i(k),j(k),v(k)) pairs.
>
> OK. So, unless i misunderstand you, this syntax is used only to update 
> values at their current positions, not to set new positions or modify 
> ones.
There could be a convention: when v(i) is %nan, the existing value could 
be unchanged and v(i) ignored.
When v(i)==0, then A's length is automatically changed. This can make 
forthcoming assignments very hazardous.

Samuel