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<TITLE> 极值、平均、总和、连乘及排序 </TITLE>
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<H1>4.2.1 极值、平均、总和、连乘及排序</H1>
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首先介绍几个分析函数，利用这些函数可以让我们在分析数据极为方便。这些函数有：最大值<FONT COLOR=#FF0000>max</FONT>，
最小值<FONT COLOR=#FF0000>min</FONT>，平均值 <FONT COLOR=#FF0000>mean</FONT>，一组数据的中位数<FONT COLOR=#FF0000>median</FONT>，总和值<FONT COLOR=#FF0000>sum</FONT>，连乘值<FONT COLOR=#FF0000>prod</FONT>，累积总和值<FONT COLOR=#FF0000>cumsum</FONT>，
累积连乘值<FONT COLOR=#FF0000>cumprod</FONT>，排序函数<FONT COLOR=#FF0000>sort</FONT>。它们的使用方式如下
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<FONT COLOR=#FF0000>max(x)</FONT> 找出<FONT COLOR=#FF0000>x</FONT>阵列的最大值
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<FONT COLOR=#FF0000>max(x,y)</FONT> 找出<FONT COLOR=#FF0000>x</FONT>及<FONT COLOR=#FF0000>y</FONT>阵列的最大值，会有二个极值分属<FONT COLOR=#FF0000>x</FONT>及<FONT COLOR=#FF0000>y</FONT>阵列
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<FONT COLOR=#FF0000>[y,i]=max(x)</FONT> 找出<FONT COLOR=#FF0000>x</FONT>阵列的最大值以<FONT COLOR=#FF0000>y</FONT>显示，其在<TT><FONT FACE="Courier New">x</FONT></TT>阵列的位置以<FONT COLOR=#FF0000>i</FONT>显示
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<FONT COLOR=#FF0000>min(x)</FONT> 找出<FONT COLOR=#FF0000>x</FONT>阵列的最小值
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<FONT COLOR=#FF0000>min(x,y)</FONT> 找出<FONT COLOR=#FF0000>x</FONT>及<FONT COLOR=#FF0000>y</FONT>阵列的最小值，会有二个极值分属<FONT COLOR=#FF0000>x</FONT>及<FONT COLOR=#FF0000>y</FONT>阵列
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<FONT COLOR=#FF0000>[y,i]=min(x)</FONT> 找出<FONT COLOR=#FF0000>x</FONT>阵列的最小值以<FONT COLOR=#FF0000>y</FONT>显示，其在<FONT COLOR=#FF0000>x</FONT>阵列的位置以<FONT COLOR=#FF0000>i</FONT>显示
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<FONT COLOR=#FF0000>mean(x)</FONT> 找出<FONT COLOR=#FF0000>x</FONT>阵列的平均值
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<FONT COLOR=#FF0000>median(x)</FONT> 找出<FONT COLOR=#FF0000>x</FONT>阵列的中位数
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<FONT COLOR=#FF0000>sum(x)</FONT> 计算<FONT COLOR=#FF0000>x</FONT>阵列的总和值
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<FONT COLOR=#FF0000>prod(x)</FONT> 计算<FONT COLOR=#FF0000>x</FONT>阵列的连乘值
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<FONT COLOR=#FF0000>cumsum(x)</FONT> 计算<FONT COLOR=#FF0000>x</FONT>阵列的累积总和值
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<FONT COLOR=#FF0000>cumprod(x)</FONT> 计算<FONT COLOR=#FF0000>x</FONT>阵列的累积连乘值
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以下是几个例子：
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<FONT COLOR=#FF0000>>> rains % rains为一个2x1的阵列</FONT>
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<FONT COLOR=#FF0000>rains =</FONT>
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<FONT COLOR=#FF0000> 126.8 148.5 173.0 148.4 194.7 208.9</FONT>
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<FONT COLOR=#FF0000> 328.8 300.7 268.3 210.5 278.4 321.5</FONT>
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<FONT COLOR=#FF0000>>> avg_rain=mean(rains) % 将rains阵列中的每一行的平均值列出</FONT>
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<FONT COLOR=#FF0000>avg_rain =</FONT>
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<FONT COLOR=#FF0000> 227.8000 224.6000 220.6500 179.4500
236.5500 265.2000</FONT>
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<FONT COLOR=#FF0000>>> avg_rain=mean(avg_rain) % 将上述阵列中的平均值列出</FONT>
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<FONT COLOR=#FF0000>avg_rain =</FONT>
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<FONT COLOR=#FF0000> 225.7083</FONT>
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<FONT COLOR=#FF0000>>> max_rain=max(rains) % 将rains阵列中的每一行的最大值列出</FONT>
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<FONT COLOR=#FF0000>max_rain =</FONT>
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<FONT COLOR=#FF0000> 328.8000 300.7000 268.3000 210.5000
278.4000 321.5000</FONT>
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<FONT COLOR=#FF0000>>> [max_rain,x]=max(rains) % 将rains阵列中的每一行的最大值及其位置列出</FONT>
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<FONT COLOR=#FF0000>max_rain =</FONT>
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<FONT COLOR=#FF0000> 328.8000 300.7000 268.3000 210.5000
278.4000 321.5000</FONT>
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<FONT COLOR=#FF0000>x =</FONT>
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<FONT COLOR=#FF0000> 2 2 2 2 2 2</FONT>
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<FONT COLOR=#FF0000>>> min_rain=min(rains) % 将rains阵列中的每一行的最小值列出</FONT>
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<FONT COLOR=#FF0000>min_rain =</FONT>
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<FONT COLOR=#FF0000> 126.8000 148.5000 173.0000 148.4000
194.7000 208.9000<BR>
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<FONT COLOR=#FF0000>>> s_sort=sort(rains) % 将rains阵列的值由小到大做排序</FONT>
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<FONT COLOR=#FF0000>s_sort =</FONT>
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<FONT COLOR=#FF0000> 126.8000 148.5000 173.0000 148.4000
194.7000 208.9000</FONT>
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<FONT COLOR=#FF0000> 328.8000 300.7000 268.3000 210.5000
278.4000 321.5000<BR>
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<FONT COLOR=#FF0000>>> x=[1 2 3 4 5];</FONT>
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<FONT COLOR=#FF0000>>> sum(x) % 将x阵列的值做总和</FONT>
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<FONT COLOR=#FF0000>ans =</FONT>
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<FONT COLOR=#FF0000> 15</FONT>
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<FONT COLOR=#FF0000>>> prod(x) % 将x阵列的值做连乘</FONT>
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<FONT COLOR=#FF0000>ans =</FONT>
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<FONT COLOR=#FF0000> 120</FONT>
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<FONT COLOR=#FF0000>>> cumsum(x) % 将x阵列的值累积后做总和</FONT>
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<FONT COLOR=#FF0000>ans =</FONT>
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<FONT COLOR=#FF0000> 1 3 6 10 15</FONT>
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<FONT COLOR=#FF0000>>> cumprod(x) % 将x阵列的值累积后做连乘</FONT>
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<FONT COLOR=#FF0000>ans =</FONT>
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<FONT COLOR=#FF0000> 1 2 6 24 120<BR>
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