ind2sub

Converting a linear index to subscripts

Usage

[s1, s2, ..., sN] = ind2sub(sizVec, I)

• sizVec is a size vector.
• I is an array containing linear indexes for the size vector sizVec. Each element of I is converted to subscripts s1, s2, ..., sN for the size vector sizVec.
• The outputs s1, s2, ..., sN have the same sizes as I, as illustrated in the figure below.

• Depending on the ndims of sizVec and N, the function has different behaviours:

  • If ndims == N, e.g., [s1,s2,s3] = ind2sub([2,3,4],3), then I is converted using sizVec.
  • If ndims < N, e.g., [s1,s2,s3] = sub2ind([2,3],3), then I is converted using sizVec and then si for i larger than ndims are all ones.
  • If ndims > N > 1, e.g., [s1, s2] = sub2ind([2 3 4 5],20), then sizVec is reshaped to a new size vector having N dimensions. More specifically, the new size vector is [sizVec(1:N - 1) prod(sizVec(N:end))]. The new size vector is then used to obtain the subscripts.
  • If N == 1, calling sub2ind(sizVec,I) directly returns I.

Example

• Convert some randomly generated linear indices to subscripts.

Input

I = randi(10,3,3)
[s1, s2] = ind2sub([2 5], I)

Output

I =
 7.000   4.000   8.000
 5.000   9.000   6.000
 2.000   2.000   6.000

s1 =
 1.000   2.000   2.000
 1.000   1.000   2.000
 2.000   2.000   2.000

s2 =
 4.000   2.000   4.000
 3.000   5.000   3.000
 1.000   1.000   3.000