Suppose I have a sparse matrix Sparstica that is a vertical concatenation of several other sparse matrices. When I type Sparstica(:), I get a list of the nonzero elements. In the left column, will be the index of the element, in the right column will be the nonzero element.
How can I manipulate the i-th and j-th non-zero element of every other sparse block matrix in the middle n-2 blocks (n sparse block matrices in total)?
Appended: To clarify what I mean by the i-th and j-th element of every other sparse matrix, suppose I have
Sparstica = [A_1; A_2; A_3; ... ; A_n]
This was created from vertcat. Now I need to take the i-th and j-th, say the 3rd and 5th, nonzero element of every other sparse matrix from A_2 to A_{N-1} (I know the notation for this actually isn't allowed, but just for demonstrative purposes). I'd like to accomplish this without using for-loops if possible.
You can find the non-zero elements using find:
>> A = speye(3)
A =
(1,1) 1
(2,2) 1
(3,3) 1
>> I = find(A ~= 0)
I =
1
5
9
If you need the indices in row/column format, use ind2sub:
>> [X, Y] = ind2sub(size(A), I)
X =
1
2
3
Y =
1
2
3