mean（求均值）,max/min（求最值）

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一、mean命令

1. mean(X)

S = mean(X) is the mean value of the elements in X if X is a vector. For matrices, S is a row vector containing the mean value of each column.

若X是行向量或列向量，则返回所有元素的平均值；
若X为矩阵，则返回每一列的平均值，等同于mean(X,1)，故mean(X,2)，返回每一行的平均值；

>> X = 1:6X =     1     2     3     4     5     6>> mean(X)ans =    3.5000%-------------------------------------------------->> X = magic(3)X =     8     1     6     3     5     7     4     9     2>> mean(X)ans =     5     5     5%-------------------------------------------------->> X = reshape(1:12,3,4)X =     1     4     7    10     2     5     8    11     3     6     9    12>> mean(X,2)ans =    5.5000    6.5000    7.5000

二、max/min命令

1. v=max(X)

For vectors (row or column), max(X) is the largest element in X. For matrices, max(X) is a row vector containing the maximum element from each column.

若果X为一个行向量或列向量，max(X)返回其中最大元素的值。

>> x = 1:7x =     1     2     3     4     5     6     7>> v = max(x)v =     7

若X为一个矩阵，max(X)返回每一列的最大值，等同于max(X,[],1)，故max(X,[],2)返回每一行的最大值。

>> XX =     8     1     6     3     5     7     4     9     2>> max(X)ans =     8     9     7>> max(X,[],1)ans =     8     9     7%------------------------------------------------->> max(X,[],2)ans =     8     7     9

2. [v,l]=max(X)

[value,Ioc] = max(X) returns the indices of the maximum values in vector I. If the values along the first non-singleton dimension contain more than one maximal element, the index of the first one is returned.

若X为一个行向量或者列向量，[value,Ioc] = max(X) 返回[最大值，最大值所在位置]；如果最大值不止一个，则返回第一个。

>> X = [23 45 78 67 5 78]X =    23    45    78    67     5    78>> [v,l] = max(X)v =    78l =     3

若X为一个矩阵，[value,Ioc] = max(X)，返回 [最大值，最大值所在行号]；如果最大值不止一个，则返回第一个，等同于[value,Ioc] = max(X,[],1)。

X =     8     9     6     3     5     7     4     9     2>> [v,l] = max(X,[],1)v =     8     9     7l =     1     1     2

min 用法同max

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