一、randperm命令

1.随机产生N个1到N的整数

P = randperm(N) returns a vector containing a random permutation of the integers 1:N. For example, randperm(6) might be [2 4 5 6 1 3].

返回一个N维向量P，包含N个1到N的随机值，且不重复！

>> P=randperm(6)P =     4     5     2     1     6     3>> P=randperm(6)P =     4     6     2     1     3     5

2.随机产生K个1到N的整数

P = randperm(N,K) returns a row vector containing K unique integers selected randomly from 1:N. For example, randperm(6,3) might be [4 2 5].

返回一个K维向量P，包含K个1到N的随机值，且不重复！

>> P=randperm(6,5)P =     1     5     6     2     3>> P=randperm(6,5)P =     5     4     3     6     2

二、reshape命令

1.重塑矩阵

reshape(X,M,N) or 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.

将矩阵Xm×n重塑成一个M×N的矩阵，按每一列从上往下取，其中m∗n=M∗N，否则将产生错误。

>> X=rand(3,4)X =    0.5519    0.4872    0.2137    0.9010    0.4038    0.3848    0.5439    0.0563    0.7501    0.0614    0.4106    0.4435>> reshape(X,4,3)ans = %注意观察是从X的每一列开始取    0.5519    0.3848    0.4106    0.4038    0.0614    0.9010    0.7501    0.2137    0.0563    0.4872    0.5439    0.4435>> reshape(X,6,2)ans =    0.5519    0.2137    0.4038    0.5439    0.7501    0.4106    0.4872    0.9010    0.3848    0.0563    0.0614    0.4435>> reshape(X,2,6)ans =    0.5519    0.7501    0.3848    0.2137    0.4106    0.0563    0.4038    0.4872    0.0614    0.5439    0.9010    0.4435

当然，矩阵X也可以用其他形式的矩阵来代替。

>> reshape(1:15,5,3)ans =     1     6    11     2     7    12     3     8    13     4     9    14     5    10    15>> reshape(1:2:16,2,4)ans =     1     5     9    13     3     7    11    15