matrix question

2011 8 16
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Q =
10 20 30 40 50 60 70
8 9 10 11 12 13 14
33 30 27 24 21 18 15
28 35 42 49 56 63 70
36 45 54 63 72 81 90
-1 -2 -3 -4 -5 -6 -7
64 69 74 79 84 89 94
required to find:
T=
64 79 94
28 49 70
10 40 70
I used syntax Q([7:21:49; 4:21:49; 16:6:49;])
but it doesn't work. I can only get
64 79 94
28 49 70
using Q([7:21:49; 4:21:49]) and it doesn't accept Q([7:21:49; 4:21:49; 16:6:49;])... any ideas?

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Dwyane Wade
Dwyane Wade 2011-8-16
I have a new answer : Q(1:3:7, [1;4;7]) which yields to:
10 40 70
28 49 70
64 79 94
now how do I flip this upside down? help me pls
Paulo Silva
Paulo Silva 2011-8-16
The flipud function does that but you can easily avoid using it, see my answer below.
Dwyane Wade
Dwyane Wade 2011-8-16
I got it now guys!
flipud(Q(1:3:7, [1;4;7]))
Thanks for the help anyway!

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Paulo Silva
Paulo Silva 2011-8-16

0 个投票

Q =[10 20 30 40 50 60 70
8 9 10 11 12 13 14
33 30 27 24 21 18 15
28 35 42 49 56 63 70
36 45 54 63 72 81 90
-1 -2 -3 -4 -5 -6 -7
64 69 74 79 84 89 94]
Q(7:-3:1,1:3:7)

3 个评论
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Dwyane Wade
Dwyane Wade 2011-8-16
Thank you sir but I've found a much efficient way of doing this :
flipud(Q(1:3:7, [1;4;7]))
I learned that from you! Thank you! :)
Paulo Silva
Paulo Silva 2011-8-16
sorry but that's not efficient at all, you are using a function without needing it.
Dwyane Wade
Dwyane Wade 2011-8-16
its ok we are allowed to use it sir. thank you for the help!

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