MATLAB学习（三）元素访问和常用代数运算

>> A=[1,2;3,4],B=[0,2;4,5]

A =

     1     2
     3     4


B =

     0     2
     4     5

>> C=A>=B

C =

     1     1
     0     0

>> D=A==B

D =

     0     1
     0     0

>> A~=B

ans =

     1     0
     1     1

>> x=-3:5;L=abs(x)>2;y=x(L)

y =

    -3     3     4     5

>> x

x =

    -3    -2    -1     0     1     2     3     4     5

>> L

L =

     1     0     0     0     0     0     1     1     1

>> 

 

>> a=[16 2 3 13;5 11 0 8;9 7 6 12;4 14 -1 2]

a =

    16     2     3    13
     5    11     0     8
     9     7     6    12
     4    14    -1     2

>> a(1:3,3)

ans =

     3
     0
     6

>> b=a(1:3,:)

b =

    16     2     3    13
     5    11     0     8
     9     7     6    12

>> x=(-1:0.2:1)

x =

  1 至 7 列

   -1.0000   -0.8000   -0.6000   -0.4000   -0.2000         0    0.2000

  8 至 11 列

    0.4000    0.6000    0.8000    1.0000

>> z=[x,sin(x)]

z =

  1 至 7 列

   -1.0000   -0.8000   -0.6000   -0.4000   -0.2000         0    0.2000

  8 至 14 列

    0.4000    0.6000    0.8000    1.0000   -0.8415   -0.7174   -0.5646

  15 至 21 列

   -0.3894   -0.1987         0    0.1987    0.3894    0.5646    0.7174

  22 列

    0.8415

>> c=magic(4)

c =

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

>> c(:,3)=[]

c =

    16     2    13
     5    11     8
     9     7    12
     4    14     1

>> k=find(A<=3)
未定义函数或变量 'A'。
 
是不是想输入:
>> k=find(a<=3) %单下标从上到下，从左到右

k =

     5
     9
    10
    12
    16

>> [s,t]=find(a<=3)

s =

     1
     1
     2
     4
     4


t =

     2
     3
     3
     3
     4

>> I=(a<=3)

I =

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

>> a(I)

ans =

     2
     3
     0
    -1
     2

>> B=a(abs(a-2)<=1)

B =

     2
     3
     2

>> A=[1,3,5;2,4,6;3,5,9]

A =

     1     3     5
     2     4     6
     3     5     9

>> B=[1,3,5;2,4,6;1,1,1]

B =

     1     3     5
     2     4     6
     1     1     1

>> dB=det(B),nA=inv(A)

dB =

     0


nA =

   -1.5000    0.5000    0.5000
   -0.0000    1.5000   -1.0000
    0.5000   -1.0000    0.5000

>> rref([A,B])

ans =

     1     0     0     0    -2    -4
     0     1     0     2     5     8
     0     0     1    -1    -2    -3

>> c=ones(3),[V,D]=eig(C)

c =

     1     1     1
     1     1     1
     1     1     1

未定义函数或变量 'C'。
 
>> C=ones(3),[V,D]=eig(C)

C =

     1     1     1
     1     1     1
     1     1     1


V =

    0.4082    0.7071    0.5774
    0.4082   -0.7071    0.5774
   -0.8165         0    0.5774


D =

   -0.0000         0         0
         0   -0.0000         0
         0         0    3.0000

>> cT=(A+i*B)',T=(A+i*B).',rT=A'

cT =

   1.0000 - 1.0000i   2.0000 - 2.0000i   3.0000 - 1.0000i
   3.0000 - 3.0000i   4.0000 - 4.0000i   5.0000 - 1.0000i
   5.0000 - 5.0000i   6.0000 - 6.0000i   9.0000 - 1.0000i


T =

   1.0000 + 1.0000i   2.0000 + 2.0000i   3.0000 + 1.0000i
   3.0000 + 3.0000i   4.0000 + 4.0000i   5.0000 + 1.0000i
   5.0000 + 5.0000i   6.0000 + 6.0000i   9.0000 + 1.0000i


rT =

     1     2     3
     3     4     5
     5     6     9