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MATLAB冒号符号

冒号(:)是最有用的运算符在MATLAB之一。它是用来创建矢量,下标数组和指定的迭代。

如果想创建一个行向量,包含从1到10的整数,如下:

1:10

MATLAB执行该语句,并返回一个行向量,包含从1到10的整数:

ans =
     1     2     3     4     5     6     7     8     9    10

如果想指定以外的一个增量值,例如:

100: -5: 50

MATLAB执行该语句,并返回以下结果:

ans =
   100    95    90    85    80    75    70    65    60    55    50

让我们再举一个例子:

0:pi/8:pi

MATLAB执行该语句,并返回以下结果:

ans =
  Columns 1 through 7
         0    0.3927    0.7854    1.1781    1.5708    1.9635    2.3562
  Columns 8 through 9
    2.7489    3.1416

可以使用冒号运算符来创建矢量指数选择行,列或数组中的元素。

下表描述了其用于此目的(让我们有一个矩阵A):

格式 目的
A(:,j) is the jth column of A.
A(i,:) is the ith row of A.
A(:,:) is the equivalent two-dimensional array. For matrices this is the same as A.
A(j:k) is A(j), A(j+1),...,A(k).
A(:,j:k) is A(:,j), A(:,j+1),...,A(:,k).
A(:,:,k) is the kth page of three-dimensional array A.
A(i,j,k,:) is a vector in four-dimensional array A. The vector includes A(i,j,k,1), A(i,j,k,2), A(i,j,k,3), and so on.
A(:) is all the elements of A, regarded as a single column. On the left side of an assignment statement, A(:) fills A, preserving its shape from before. In this case, the right side must contain the same number of elements as A.

例子

创建一个脚本文件,并键入下面的代码:

A = [1 2 3 4; 4 5 6 7; 7 8 9 10]
A(:,2)      % second column of A
A(:,2:3)    % second and third column of A
A(2:3,2:3)  % second and third rows and second and third columns

当您运行该文件,它会显示以下结果:

A =
     1     2     3     4
     4     5     6     7
     7     8     9    10

ans =
     2
     5
     8

ans =
     2     3
     5     6
     8     9

ans =
     5     6
     8     9