>> gradeofgroup1=[95 87 89;65 70 76; 88 90 92; 94 55 78];
gradeofgroup2=[86 89 75;85 65 77; 78 80 95; 93 75 88];
gradeofgroup=horzcat(gradeofgroup1,gradeofgroup2)

gradeofgroup =

95 87 89 86 89 75
65 70 76 85 65 77
88 90 92 78 80 95
94 55 78 93 75 88

>> gradeofgroup=vertcat(gradeofgroup1,gradeofgroup2)

gradeofgroup =

95 87 89
65 70 76
88 90 92
94 55 78
86 89 75
85 65 77
78 80 95
93 75 88

>> max(gradeofgroup)
min(gradeofgroup)

ans =

95 90 95

ans =

65 55 75

>> gradeofgroup([1,3],:)=gradeofgroup([3,1],:)

gradeofgroup =

88 90 92
65 70 76
95 87 89
94 55 78
86 89 75
85 65 77
78 80 95
93 75 88

>> clear gradeofgroup([1,3],:)=gradeofgroup([3,1],:)
>> gradeofgroup

gradeofgroup =

88 90 92
65 70 76
95 87 89
94 55 78
86 89 75
85 65 77
78 80 95
93 75 88

>> gradeofgroup([2,7],:)=gradeofgroup([7,2],:)

gradeofgroup =

95 87 89
78 80 95
88 90 92
94 55 78
86 89 75
85 65 77
65 70 76
93 75 88

>> gradeofgroup(:,1)=gradeofgroup(:,1)+1
gradeofgroup(:,3)=gradeofgroup(;,3)+1

gradeofgroup =

96 87 89
79 80 95
89 90 92
95 55 78
87 89 75
86 65 77
66 70 76
94 75 88

>> gradeofgroup=vertcat(gradeofgroup1,gradeofgroup2)

gradeofgroup =

95 87 89
65 70 76
88 90 92
94 55 78
86 89 75
85 65 77
78 80 95
93 75 88

>> gradeofgroup([2,7],:)=gradeofgroup([7,2],:)

gradeofgroup =

95 87 89
78 80 95
88 90 92
94 55 78
86 89 75
85 65 77
65 70 76
93 75 88

>> sort(gradeofgroup(:,2),'descend')

ans =

90
89
87
80
75
70
65
55

>> sort(gradeofgroup,2,'descend')

ans =

96 90 87
96 80 79
93 90 89
95 79 55
89 87 76
86 78 65
77 70 66
94 89 75

第五题完全没明白......