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3.3 Object Sizes
The following functions allow you to determine the size of a variable or
expression. These functions are defined for all objects. They return
1 when the operation doesn't make sense. For example, Octave's
data structure type doesn't have rows or columns, so the rows
and
columns
functions return 1 for structure arguments.
 Builtin Function: ndims (a)
Returns the number of dimensions of array a. For any array, the result will always be larger than or equal to 2. Trailing singleton dimensions are not counted.
 Builtin Function: columns (a)
Return the number of columns of a.
See also: size, numel, rows, length, isscalar, isvector, ismatrix.
 Builtin Function: rows (a)
Return the number of rows of a.
See also: size, numel, columns, length, isscalar, isvector, ismatrix.
 Builtin Function: numel (a)
Returns the number of elements in the object a.
See also: size.
 Builtin Function: length (a)
Return the `length' of the object a. For matrix objects, the length is the number of rows or columns, whichever is greater (this odd definition is used for compatibility with MATLAB).
 Builtin Function: size (a, n)
Return the number rows and columns of a.
With one input argument and one output argument, the result is returned in a row vector. If there are multiple output arguments, the number of rows is assigned to the first, and the number of columns to the second, etc. For example,
size ([1, 2; 3, 4; 5, 6]) ⇒ [ 3, 2 ] [nr, nc] = size ([1, 2; 3, 4; 5, 6]) ⇒ nr = 3 ⇒ nc = 2
If given a second argument,
size
will return the size of the corresponding dimension. For examplesize ([1, 2; 3, 4; 5, 6], 2) ⇒ 2
returns the number of columns in the given matrix.
See also: numel.
 Builtin Function: isempty (a)
Return 1 if a is an empty matrix (either the number of rows, or the number of columns, or both are zero). Otherwise, return 0.
 Builtin Function: isnull (x)
Return 1 if x is a special null matrix, string or single quoted string. Indexed assignment with such a value as righthand side should delete array elements. This function should be used when overloading indexed assignment for userdefined classes instead of
isempty
, to distinguish the cases:
A(I) = []
This should delete elements if
I
is nonempty.
X = []; A(I) = X
This should give an error if
I
is nonempty.

 Builtin Function: size_equal (a, b, …)
Return true if the dimensions of all arguments agree. Trailing singleton dimensions are ignored. Called with a single argument, size_equal returns true.
 Builtin Function: squeeze (x)
Remove singleton dimensions from x and return the result. Note that for compatibility with MATLAB, all objects have a minimum of two dimensions and row vectors are left unchanged.
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