size（）：获取矩阵的行数和列数 （1）s=size(A),
当只有一个输出参数时，返回一个行向量，该行向量的第一个元素时矩阵的行数，第二个元素是矩阵的列数。
（2）[r,c]=size(A),
当有两个输出参数时，size函数将矩阵的行数返回到第一个输出变量r，将矩阵的列数返回到第二个输出变量c。
（3）size(A,n)如果在size函数的输入参数中再添加一项n，并用1或2为n赋值，则 size将返回矩阵的行数或列数。其中r=size(A,1)该语句返回的时矩阵A的行数， c=size(A,2) 该语句返回的时矩阵A的列数。
另外，length()=max(size()).

MATLAB help 解释 ：
>> help size
sizeSize 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) for N>1 returns the sizes of the first N
dimensions of the 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 dimensions N
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. If DIM > NDIMS(X), M will be 1.

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.

Example:
If
X = rand(2,3,4);
then
d = size(X)returnsd = [2 3 4]
[m1,m2,m3,m4] = size(X)returnsm1 = 2, m2 = 3, m3 = 4, m4 = 1
[m,n] = size(X) returnsm = 2, n = 12
m2 = size(X,2)returnsm2 = 3