MATLAB示例(2)

A = [1:4;5:8;9:12;13:16] x = A(2:3,3:4)%子阵访问1 y = A([2:3;3:4])%子阵访问2 A =

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 x =

7 8 11 12 y =

5 9 9 13

A = [1:4;5:8;9:12;13:16] x = A(2,:)%获取单行 y = A(:,2:3)%获取多列 A =

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 x =

5 6 7 8 y =

2 3 6 7 10 11 14 15

1.3.2 利用逻辑矩阵访问

A = [1:4;5:8;9:12;13:16] B = A>10 x = A(B) A(A>10)=0 A =

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

B =

0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 x = 13 14 11 15 12 16 A =

1 2 3 4 5 6 7 8 9 10 0 0 0 0 0 0

1.4 矩阵拼接、变形，改变大小

1.4.1 矩阵拼接

a = ones(3,4) b = zeros(3,2)

c = [a b] %水平方向连接，行数一致

x = [ones(3,4); zeros(2,4)] %垂直方向连接，列数一致 a =

1 1 1 1 1 1 1 1 1 1 1 1 b =

0 0 0 0 0 0 c =

1 1 1 1 0 0 1 1 1 1 0 0 1 1 1 1 0 0

x =

1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 A = ones(4) B = zeros(4)

C = cat(3,A,B)%三维矩阵 A =

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 B =

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 C(:,:,1) =

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 C(:,:,2) =

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

1.4.2 矩阵变形

A = 1:16

B = reshape(A,2,8)%元素个数不变，保持矩形C = reshape(A,4,4) A =

Columns 1 through 10

1 2 3 4 5 6 7 8 9 10 Columns 11 through 16

11 12 13 14 15 16 B =

1 3 5 7 9 11 13 15 2 4 6 8 10 12 14 16 C =

1 5 9 13 2 6 10 14 3 7 11 15 4 8 12 16

1.4.3 矩阵90度旋转

A = reshape(1:9,3,3) B = rot90(A,1)%逆时针 C = rot90(A,-1)%顺时针 A =

1 4 7 2 5 8 3 6 9 B =

7 8 9 4 5 6 1 2 3 C =

3 2 1 6 5 4 9 8 7

1.4.4 矩阵翻转

A = reshape(1:9,3,3) B = fliplr(A)%左右翻转 C = flipud(A)%上下翻转 A =

1 4 7 2 5 8

3 6 9 B =

7 4 1 8 5 2 9 6 3 C =

3 6 9 2 5 8 1 4 7

1.4.5 矩阵转置

A = reshape(1:9,3,3) B = A'%共轭转置 C = A.' A =

1 4 7 2 5 8 3 6 9 B =

1 2 3 4 5 6 7 8 9 C =

1 2 3 4 5 6 7 8 9

1.4.6 矩阵扩容

A = reshape(1:9,3,3) A(4,:) = 10:12%增加第4行

A(:,4) = [10;20;30;40]%增加第4列 A =

1 4 7 2 5 8

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