`sub2ind`

Converts row and column subscripts to linear indices.

Category: Language Fundamentals > Matrices and Arrays

Syntax

ind = sub2ind(sz, I, J)

Returns the linear index of element (I,J) in an array of size sz.

ind = sub2ind(sz, I1, I2, ..., In)

Same for an N-dimensional array.

Description

MATLAB stores arrays column by column, so the element at row i and column j of an m-row matrix has linear index i + (j-1)*m. sub2ind applies that rule for any number of dimensions and checks that the subscripts are in range.

It is handy for picking scattered elements, such as a diagonal or a list of points, with a single index vector.

Input arguments

sz: Size vector of the array, for example [3 4].
I, J: Subscript arrays of identical size. Each value must be a positive integer within the matching dimension of sz.

Output arguments

ind: Linear indices, same size as the subscript arguments.

Example

M = magic(4);
k = sub2ind(size(M), [1 2 3], [2 3 4])
M(k)

Output

k = 1×3

     5    10    15
ans = 1×3

     2    10    12

sub2ind