Hello,
diag works both ways:
Le 17/06/2015 09:22, [email protected] a écrit :
No
A basic example:
-->A = [1 0 0 0 ; 0 6 0 0 ; 0 0 -5 0 ; 0 0 0 31]
A =
1. 0. 0. 0.
0. 6. 0. 0.
0. 0. - 5. 0.
0. 0. 0. 31.
-->B = diag(A)
B =
1.
6.
- 5.
31.
-->A = [1 0 0 0 ; 0 6 0 0 ; 0 0 -5 0 ; 0 0 0 31]
A =
1. 0. 0. 0.
0. 6. 0. 0.
0. 0. - 5. 0.
0. 0. 0. 31.
-->B = diag(A)
B =
1.
6.
- 5.
31.
-->C = diag(B)
C =
1. 0. 0. 0.
0. 6. 0. 0.
0. 0. - 5. 0.
0. 0. 0. 31.
how a rebuild A from B ....
NB:
- the purpose is to find a basic but fast way to build a symmetrical matrix
using the following syntax for example : K = K +Kd + K'
- where K is the triangle upper (or lower) matrix and Kd is the diagonal
- I want to decrease the amount of memory in avoiding to use a (nxn) matrix
Paul
----- Mail d'origine -----
De: [email protected] <[email protected]>
À: [email protected]
Envoyé: Wed, 17 Jun 2015 09:14:39 +0200 (CEST)
Objet: Re: [Scilab-users] opposite to 'diag' keyword
Hello,
Le 17/06/2015 09:05, [email protected] a écrit :
The question is quite basic: I'm trying to opposite to 'diag' keyword in order
to build a diagonal matrix from a vector, but I fail so far ... what is the
trick?
The diag help says "diagonal including or extracting"
> diag([1 2])
gives the matrix [1 0;0 2]
Is it the "opposite" you want?
--Jean-Yves
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