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