reshape把指定的矩阵改变形状，但是元素个数不变，
例如，行向量：
a = [1 2 3 4 5 6]
执行下面语句把它变成3行2列：
b = reshape(a,3,2)
执行结果：
b =
1 4
2 5
3 6
若a=[1 2 3
4 5 6
7 8 9]
可以从b中看到reshape是按列来读取的，如
a=[1 2 ; 3 4]
如果使用b=reshape(a,1,4)
则得到的结果是
b=[1 3 2 4]
如果想得到
b=[1 2 3 4]
需要使用
b=reshape(a',1,4)
因为reshape使用的列优先！
b转化回去是同样的道理。
使用reshpe后想得到b=[1 2 3 4 5 6 7 8 9]
只需要将a转置一下就可以了：
b=reshape(a',1,9)
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matlab中的解释如下：
RESHAPE Change size.
RESHAPE(X,M,N) returns the M-by-N matrix whose elements
are taken columnwise from X. An error results if X does
not have M*N elements.
RESHAPE(X,M,N,P,...) returns an N-D array with the same
elements as X but reshaped to have the size M-by-N-by-P-by-...
M*N*P*... must be the same as PROD(SIZE(X)).
RESHAPE(X,[M N P ...]) is the same thing.
RESHAPE(X,...,[],...) calculates the length of the dimension
represented by [], such that the product of the dimensions
equals PROD(SIZE(X)). PROD(SIZE(X)) must be evenly divisible
by the product of the known dimensions. You can use only one
occurrence of [].
In general, RESHAPE(X,SIZ) returns an N-D array with the same
elements as X but reshaped to the size SIZ. PROD(SIZ) must be
the same as PROD(SIZE(X)).