MATLAB中size（A，2）什么意思

size(A, 2)表示取矩阵A的列数。如果A是多维矩阵，则表示的仍然是取每个二维矩阵的列数。

举例说明如下：

% 如果A是2维矩阵（行向量或列向量可看为行数或列数为1的矩阵）
A=[1, 2, 3; 4, 2, 3];
col = size(A, 2);  % 计算结果为col=3，因为矩阵A的列数为3

% 如果A是多维矩阵（以3维矩阵为例）
A(:, :, 1)=[1, 2, 3; 4, 2, 3];
A(:, :, 2)=[4, 2, 2; 6, 2, 4];
col = size(A, 2);  % col的值仍然为3，因为三维矩阵A的每个2维矩阵都有3列

A的第二维的大小。

help size
SIZE Size of array.
D = SIZE(X), for M-by-N matrix X, returns the two-element
row vector D = [M, N] containing the number of rows and columns
in the matrix. For N-D arrays, SIZE(X) returns a 1-by-N
vector of dimension lengths. Trailing singleton dimensions
are ignored.

[M,N] = SIZE(X) for matrix X, returns the number of rows and
columns in X as separate output variables.

[M1,M2,M3,...,MN] = SIZE(X) returns the sizes of the first N
dimensions of array X. 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), MN contains the product of the sizes of the
remaining dimensions, i.e., dimensions N+1 through
NDIMS(X).

M = SIZE(X,DIM) returns the length of the dimension specified
by the scalar DIM. For example, SIZE(X,1) returns the number
of rows.

When SIZE is applied to a Java array, the number of rows
returned is the length of the Java array and the number of columns
is always 1. When SIZE is applied to a Java array of arrays, the
result describes only the top level array in the array of arrays.
在matlab里输入help size 可看，size（A，2）是返回A矩阵第二列元素个数

不是A的第二维的大小。