1
$\begingroup$

I got confused by {i_, j_} /; in the following code. I didn't see an explanation in the SparseArray documentation. Can anyone tell me how this part work in the code?

m1 = SparseArray[{{i_, i_} -> -2, {i_, j_} /; Abs[i - j] == 1 -> 1}, {5, 5}];
$\endgroup$

1 Answer 1

2
$\begingroup$

{i_, j_} /; Abs[i - j] == 1 is a pattern. It matches pairs of expressions the difference of which is 1.

/; is Condition.

In SparseArray this will put a 1 on the second diagonals, as the difference of the indices of elements on the second diagonals is 1 or -1.

$\endgroup$
1
  • $\begingroup$ @Szaolcs Thanks a lot! $\endgroup$
    – Lawerance
    Jul 26, 2014 at 18:21

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.