Creating a Matrix that is a manipulation of another matrix
4 vues (au cours des 30 derniers jours)
Afficher commentaires plus anciens
Hi, I'm very new to Matlab, and I have a question about creating a matrix. If there is a matrix A = [a b ; c d], how do you create a matrix = [a -b ; c -d]? So the second column entries of A are multiplied by -1.
Thank you.
0 commentaires
Réponse acceptée
dpb
le 6 Oct 2015
A(:,2)=-A(:,2); % negate elements in original
or
A(:,2)=-1*A(:,2);
or
B=[A(:,1) -A(:,2}]; % new array keeping old
Any number of additional ways are possible including, of course linear algebra methods...
B=A*[1 0;0 -1];
0 commentaires
Plus de réponses (4)
Joseph Cheng
le 6 Oct 2015
Modifié(e) : Joseph Cheng
le 6 Oct 2015
There are lots of ways how about element by element multiplication like:
x = magic(4)
trans = [ones(4,2) -ones(4,2)]
x.*trans
which if it gets complicated say corners and such you can build the trans matrix to whatever you want.
or by selecting the columns manually:
x(:,3:4) = -x(:,3:4)
0 commentaires
Julian
le 6 Oct 2015
1 commentaire
Joseph Cheng
le 6 Oct 2015
so the indexing is something you should spend some time to read about to fully understand but its like:
x(row,column) so you can say x(2,3) which will specifically be the element of intersection of row 2 and column 3. so to replace one element you would just specify that one element. the : marker in the examples everyone is giving is the "all" marker for all rows/columns (depending on where it is)
x(:,2) is all rows in column 2
x(2,:) is for all columns for row 2.
Voir également
Catégories
En savoir plus sur Multidimensional Arrays dans Help Center et File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!