练习三

一、

>> A=magic(3)

A =

     8     1     6
     3     5     7
     4     9     2

>> A(3,4)=0

A =

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

>> B=rand(3,4)

B =

    0.8147    0.9134    0.2785    0.9649
    0.9058    0.6324    0.5469    0.1576
    0.1270    0.0975    0.9575    0.9706


>> C=[A,B]

C =

    8.0000    1.0000    6.0000         0    0.8147    0.9134    0.2785    0.9649
    3.0000    5.0000    7.0000         0    0.9058    0.6324    0.5469    0.1576
    4.0000    9.0000    2.0000         0    0.1270    0.0975    0.9575    0.9706

>> D=[A;B]

D =

    8.0000    1.0000    6.0000         0
    3.0000    5.0000    7.0000         0
    4.0000    9.0000    2.0000         0
    0.8147    0.9134    0.2785    0.9649
    0.9058    0.6324    0.5469    0.1576
    0.1270    0.0975    0.9575    0.9706


>> E=C(:,[3,5])

E =

    6.0000    0.8147
    7.0000    0.9058
    2.0000    0.1270

二、

>> F=C'

F =

    8.0000    3.0000    4.0000
    1.0000    5.0000    9.0000
    6.0000    7.0000    2.0000
         0         0         0
    0.8147    0.9058    0.1270
    0.9134    0.6324    0.0975
    0.2785    0.5469    0.9575
    0.9649    0.1576    0.9706

三、

>> a=eye(4)

a =

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

>> a_down=tril(a)

a_down =

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

>> a_up=a-a_down

a_up =

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

四、

>> a=rand(4,5)

a =

    0.8173    0.2599    0.1818    0.8693    0.8530
    0.8687    0.8001    0.2638    0.5797    0.6221
    0.0844    0.4314    0.1455    0.5499    0.3510
    0.3998    0.9106    0.1361    0.1450    0.5132

>> l1=find(a(1,:)>0.3)

l1 =

     1     4     5

>> l2=find(a(2,:)>0.3)

l2 =

     1     2     4     5

>> b=[a(1,l1),a(2,l2)]

b =

    0.8173    0.8693    0.8530    0.8687    0.8001    0.5797    0.6221