MATLAB Function Reference

size

Array dimensions

Syntax

• d = size(X)
  [m,n] = size(X)
  m = size(X,dim)
  [d1,d2,d3,...,dn] = size(X)
  

Description

d = size(X) returns the sizes of each dimension of array X in a vector d with ndims(X) elements.

[m,n] = size(X) returns the size of matrix X in separate variables m and n.

m = size(X,dim) returns the size of the dimension of X specified by scalar dim.

[d1,d2,d3,...,dn] = size(X) returns the sizes of the first n dimensions of array X in separate variables.

If the number of output arguments n does not equal ndims(X), then for:

n > ndims(X)	size returns ones in the "extra" variables, i.e., outputs ndims(X)+1 through n.
n < ndims(X)	dn contains the product of the sizes of the remaining dimensions of X, i.e., dimensions n+1 through ndims(X).

Note    For a Java array, size returns the length of the Java array as the number of rows. The number of columns is always 1. For a Java array of arrays, the result describes only the top level array.

Examples

Example 1. The size of the second dimension of rand(2,3,4) is 3.

• m = size(rand(2,3,4),2)
  
  m =
       3
  

Here the size is output as a single vector.

• d = size(rand(2,3,4))
  
  d =
       2     3     4
  

Here the size of each dimension is assigned to a separate variable.

• [m,n,p] = size(rand(2,3,4))
  m =
       2
  
  n =
       3
  
  p =
       4
  

Example 2. If X = ones(3,4,5), then

• [d1,d2,d3] = size(X)
  
  d1 =       d2 =       d3 =
       3          4          5
  

But when the number of output variables is less than ndims(X):

• [d1,d2] = size(X)
  
  d1 =       d2 =
       3          20
  

The "extra" dimensions are collapsed into a single product.

If n > ndims(X), the "extra" variables all represent singleton dimensions:

• [d1,d2,d3,d4,d5,d6] = size(X)
  
  d1 =       d2 =       d3 =
       3          4          5
  
  d4 =       d5 =       d6 =
       1          1          1
  

See Also

exist, length, whos

sinh

size (serial)