numel - Number of elements in array or subscripted array expression
Syntax
n = numel(A)
n = numel(A, index1, index2, ...
indexn)
Description
n = numel(A) returns the
number of elements, n, in array A.
n = numel(A, index1, index2, ...
indexn) returns the number of subscripted elements, n, in A(index1, index2, ..., indexn). To handle the variable number of arguments, numel is typically written with the header function n = numel(A,
varargin), where varargin is a cell array
with elements index1, index2, ... indexn.
The MATLAB software implicitly calls the numel built-in function whenever an expression generates
a comma-separated list. This includes brace indexing (i.e., A{index1,index2,...,indexN}), and dot indexing (i.e., A.fieldname).
Remarks
It is important to note the significance of numel with regards to the overloaded subsref and subsasgn functions. In
the case of the overloaded subsref function for
brace and dot indexing (as described in the last paragraph), numel is used to compute the number of expected outputs
(nargout) returned from subsref. For the overloaded subsasgn function, numel is used to compute the number
of expected inputs (nargin)
to be assigned using subsasgn. The nargin value for the overloaded subsasgn function is
the value returned by numel plus 2 (one for the
variable being assigned to, and one for the structure array of subscripts).
As a class designer, you must ensure that the value of n returned by the built-in numel function
is consistent with the class design for that object. If n is different from either the nargout for the
overloaded subsref function or the nargin for the overloaded subsasgn function, then you
need to overload numel to return a value of n that is consistent with the class' subsref and subsasgn functions. Otherwise, MATLAB produces
errors when calling these functions.
Examples
Create a 4-by-4-by-2 matrix. numel counts
32 elements in the matrix.
a = magic(4);
a(:,:,2) = a'
a(:,:,1) =
16 2 3 13
5 11 10 8
9 7 6 12
4 14 15 1
a(:,:,2) =
16 5 9 4
2 11 7 14
3 10 6 15
13 8 12 1
numel(a)
ans =
32See Also
nargin, nargout, prod, size, subsasgn, subsref
 | numberOfTiles (Tiff) | | nzmax |  |
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