MatLab手记

1.读取excel

[A,B]=xlsread('xxx.xlsx','sheet1')

其中A，B为2个二维数组。A保存所有数字信息，B保存所有字符串信息。

2. 二维数组的引用

atlab中数组元素引用有三种方法：
1.下标法(subscripts)
2.索引法(index)
3.布尔法(Boolean)

Matlab中数组元素是按列存储(与Fortran一样)，比如说下面的二维数组
A=
<wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left">8</span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left">1</span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left">6</span><br style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left">3</span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left">5</span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left">7</span><br style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left">4</span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left">9</span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left">2</span><br style="text-align:left"><span style="text-align:left">Matlab的存储顺序是8,3,4,1,5,9,6,7,2，也就是说</span><span style="word-wrap:normal; word-break:normal; text-align:left">先行后列</span><span style="text-align:left">，3维数组就是</span><span style="word-wrap:normal; word-break:normal; text-align:left">先行后列再页</span><br style="text-align:left"><span style="text-align:left">Element Index Subscripts</span><br style="text-align:left"><span style="text-align:left">8</span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"> </span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left">1</span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"><wbr style="text-align:left"><span style="text-align:left"> </span></wbr></span><span style="text-align:left">(1,1)</span><br style="text-align:left"><span style="text-align:left">3</span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"><wbr style="text-align:left"><span style="text-align:left"> </span></wbr></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left">2</span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"><wbr style="text-align:left"><span style="text-align:left"> </span></wbr></span><wbr style="text-align:left"><span style="text-align:left">(2,1)</span><br style="text-align:left"><span style="text-align:left">4</span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"><wbr style="text-align:left"><span style="text-align:left"> </span></wbr></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left">3</span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"><wbr style="text-align:left"><span style="text-align:left"> </span></wbr></span><wbr style="text-align:left"><span style="text-align:left">(3,1)</span><br style="text-align:left"><span style="text-align:left">1</span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"><wbr style="text-align:left"><span style="text-align:left"> </span></wbr></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left">4</span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"><wbr style="text-align:left"><span style="text-align:left"> </span></wbr></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left">(1,2)</span><br style="text-align:left"><span style="text-align:left">5</span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"><wbr style="text-align:left"><span style="text-align:left"> </span></wbr></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left">5</span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"><wbr style="text-align:left"><span style="text-align:left"> </span></wbr></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left">(2,2)</span><br style="text-align:left"><span style="text-align:left">9</span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"><wbr style="text-align:left"><span style="text-align:left"> </span></wbr></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left">6</span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"><wbr style="text-align:left"><span style="text-align:left"> </span></wbr></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left">(3,2)</span><br style="text-align:left"><span style="text-align:left">6</span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"><wbr style="text-align:left"><span style="text-align:left"> </span></wbr></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left">7</span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"><wbr style="text-align:left"><span style="text-align:left"> </span></wbr></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left">(1,3)</span></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>
7<wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"><wbr style="text-align:left"><span style="text-align:left"> </span></wbr></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left">8</span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"><wbr style="text-align:left"><span style="text-align:left"> </span></wbr></span><wbr style="text-align:left"><span style="text-align:left">(2,3)</span><br style="text-align:left"><span style="text-align:left">2</span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"><wbr style="text-align:left"><span style="text-align:left"> </span></wbr></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left">9</span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"></span><wbr style="text-align:left"><span style="text-align:left"><wbr style="text-align:left"><span style="text-align:left"> </span></wbr></span><wbr style="text-align:left"><span style="text-align:left">(3,3)</span></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

如果我要引用第一列数据：

data = A(1:n, 1:1)

如果要转换成一行：

data = data'

3 函数拟合、绘制

1 多项式函数拟合：a=polyfit(xdata,ydata,n)

其中n表示多项式的最高阶数，xdata，ydata为将要拟合的数据，数组的方式输入．输出参数a为拟合多项式的系数
多项式在x处的值y可用下面程序计算．
y=polyval(a,x)

2 一般的曲线拟合：p=curvefit(‘Fun’,p0,xdata,ydata)
其中Fun表示函数Fun(p,data)的M函数文件，p0表示函数的初值．
若要求解点x处的函数值可用程序f=Fun(p,x)计算．
例：
t=[l：16]；

％数据输人
y=[ 4 6．4 8 8．4 9．28 9．5 9．7 9．86 10．2 10．32 10．42 10．5 10．55 10．58 10．6]；
画散点图
plot(t,y,’o’)

％(二次多项式拟合）
p=polyfit(t,y,2)

%计算结果：二次多项式的系数
p=-0.0445 1.0711 4.3252

由此得到y与t的拟合函数。

3.多元曲线拟合：

例如有x，y，z，w 这4个自变量的函数fun去拟合数据data，则：

[p,nor] = lsqcurvefit('fun', c, [x;y;z;w], data)

p为fun待定系数初值，nor为方差。

注意这里的x，y，z，w都为行向量！