matlab中size()的用法

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本文详细介绍了Matlab中size函数的使用方法，包括如何获取矩阵的行数和列数、如何将矩阵的尺寸分配给多个变量等。同时，还解释了在不同情况下size函数的行为差异。

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size(A)函数是用来求矩阵的大小的,你必须首先弄清楚A到底是什么，大小是多少。

比如说一个A是一个3×4的二维矩阵：

1、size（A） %直接显示出A大小

输出：ans=

3 4

2、s=size（A）%返回一个行向量s，s的第一个元素是矩阵的行数，第二个元素是矩阵的列数

输出：s=

3 4

3、[r,c]=size（A）%将矩阵A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

输出：r=

4、[r,c,m]=size（A）

输出：r=

也就说它把二维矩阵当作第三维为1的三维矩阵，这也如同我们把n维列向量当作n×1的矩阵一样

5、当a是一个n维行向量时，size（A）把其当成一个1×n的矩阵，因此size（a）的结果是

ans

1 n

而不是a的元素个数n

6、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)该语句返回的是矩阵A的行数， c=size(A,2) 该语句返回的是矩阵A的列数。

matlab中的解释如下：

Syntax

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

Description

d = size(X) returns thesizes of each dimension of array X in a vector d with ndims(X) elements.If X is a scalar, which MATLAB software regardsas a 1-by-1 array, size(X) returns the vector [11].

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

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

[d1,d2,d3,...,dn] = size(X), for n >1, returns the sizes of the dimensions of the array X inthe variables d1,d2,d3,...,dn, provided the number of output arguments n equals ndims(X).If n does not equal ndims(X),the following exceptions hold:

`n < ndims(X)`	`di` equals the size of the `i`thdimension of `X` for , but `dn` equalsthe product of the sizes of the remaining dimensions of `X,` thatis, dimensions `n` through `ndims(X)`.
`n > ndims(X`)	`size` returns ones in the "extra"variables, that is, those corresponding to `ndims(X)+1`through `n`.

Note For a Java array, size returns the lengthof the Java array as the number of rows. The number of columns isalways 1. For a Java array of arrays, the result describes only thetop level array.

Examples

Example 1

The size of the second dimension of rand(2,3,4) is3.

m = <span class="highlight0">size</span>(rand(2,3,4),2)

m =
     3

Here the size is output as a single vector.

d = <span class="highlight0">size</span>(rand(2,3,4))

d =
     2     3     4

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

[m,n,p] = <span class="highlight0">size</span>(rand(2,3,4))
m =
     2

n =
     3

p =
     4

Example 2

If X = ones(3,4,5), then

[d1,d2,d3] = <span class="highlight0">size</span>(X)

d1 =       d2 =       d3 =
     3          4          5

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

[d1,d2] = <span class="highlight0">size</span>(X)

d1 =       d2 =
     3          20

The "extra" dimensions are collapsed into a singleproduct.

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

[d1,d2,d3,d4,d5,d6] = <span class="highlight0">size</span>(X)

d1 =       d2 =       d3 =
     3          4          5

d4 =       d5 =       d6 =
     1          1          1