sub2ind - Convert subscripts to linear indices - MATLAB (original) (raw)

Convert subscripts to linear indices

Syntax

Description

[ind](#mw%5F5260ba83-8e04-4ee8-a636-c078dd40ef98) = sub2ind([sz](#mw%5Fddeff116-73c4-4c56-87a4-1a31fe0006fa),[row](#mw%5F54c1f6bc-22a7-4810-aa59-2d564d5173e9),[col](#mw%5F4ca15746-0835-4994-ae43-6c013ab0e04a)) returns the linear indices ind corresponding to the row and column subscripts in row and col for a matrix of sizesz. Here sz is a vector with two elements, wheresz(1) specifies the number of rows and sz(2) specifies the number of columns.

example

[ind](#mw%5F5260ba83-8e04-4ee8-a636-c078dd40ef98) = sub2ind([sz](#mw%5Fddeff116-73c4-4c56-87a4-1a31fe0006fa),[I1,I2,...,In](#mw%5F20e89540-0f9a-4754-bd27-716ed64497c7)) returns the linear indices ind corresponding to multidimensional subscripts in n arrays I1,I2,...,In for a multidimensional array of size sz. Here sz is a vector with n elements that specifies the size of each array dimension.

example

Examples

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The mapping from subscripts (indexing by position) to linear indices for a 3-by-3 matrix can be illustrated as in the following.

Specify the row and column subscripts in a 3-by-3 matrix. Convert the subscripts to linear indices.

row = [1 2 3 1]; col = [2 2 2 3]; sz = [3 3]; ind = sub2ind(sz,row,col)

The mapping from subscripts to linear indices for a 2-by-2-by-2 array can be illustrated as in the following.

Specify the row, column, and page subscripts in a 2-by-2-by-2 array. Convert the subscripts to linear indices.

I1 = [1 2 1 2]; I2 = [2 2 1 1]; I3 = [1 1 2 2]; sz = [2 2 2]; ind = sub2ind(sz,I1,I2,I3)

Convert a subscript index of a 3-D array to a single linear index.

Create an array, and find the linear index corresponding to the element in the (2,1,2) position.

A = rand(3,4,2); linearInd = sub2ind(size(A),2,1,2)

Check that both index versions refer to the same element.

Input Arguments

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Size of array, specified as a vector of positive integers. Each element of this vector indicates the size of the corresponding dimension. For example, [2 3 4] defines a 2-by-3-by-4 array.

Row subscripts, specified as a scalar, vector, matrix, or multidimensional array.row and col can be arrays of the same size, or either one can be scalar.

Column subscripts, specified as a scalar, vector, matrix, or multidimensional array.row and col can be arrays of the same size, or either one can be scalar.

Multidimensional subscripts, specified as a scalar, vector, matrix, or multidimensional array. I1,I2,…,In can be arrays of the same size, or any of them can be scalar.

Output Arguments

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Linear indices, returned as a scalar, vector, matrix, or multidimensional array.

If the subscript inputs all have the same size, then ind is also that size.
If the subscript inputs are a mix of scalars and arrays, thenind has the size of the nonscalar subscript inputs.

Data Types: double

Algorithms

For an array A, if ind = sub2ind(size(A),I1,…,In), then A(ind(k)) = A(I1(k),…,In(k)) for all k.

Extended Capabilities

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Thesub2ind function fully supports tall arrays. For more information, see Tall Arrays.

Usage notes and limitations:

The input vectors sz, row, andcol can contain only finite integer values.
The input vector sz must be fixed size at code generation time.
For code generation, the maximum number of elements in an array is constrained by the code generator and the target hardware. See Array Size Restrictions for Code Generation (MATLAB Coder). The size vector sz is not supported for arrays with more than the maximum number of elements.

Usage notes and limitations:

The first argument must be a valid size vector. Code generation does not support size vectors for arrays with more than intmax elements.

The sub2ind function fully supports GPU arrays. To run the function on a GPU, specify the input data as a gpuArray (Parallel Computing Toolbox). For more information, see Run MATLAB Functions on a GPU (Parallel Computing Toolbox).

Version History

Introduced before R2006a

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sub2ind now leverages scalar expansion and accepts a mix of scalars and vectors for subscript inputs. For example,sub2ind(sz,[1 2 3],2) is now the same as sub2ind(sz,[1 2 3],[2 2 2]). Previously, the subscript inputs were required to be the same size.