Two basic questions in matlab

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Amit Kumar
Amit Kumar 2014-11-5
评论： Amit Kumar 2014-11-6
Hello all, I used matlab for some time, but this did not made me thorough with basics.
1. If I have two matrices, I1 3x3 and I2 4x4. How I can concatenate them? Is it possible? If I do [I1,I2] it will not work as both have different dimensions.
2. If I have array of 100 random numbers and I want every 4th element starting from 20th location till end, can I do this? I want to do this without any loops.
Any ideas very welcome! Thanks in advance!!
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Adam
Adam 2014-11-5
What would you expect to be the result of concatenating a 3*3 matrix with a 4*4 matrix?

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Matt Tearle
Matt Tearle 2014-11-5
编辑：Matt Tearle 2014-11-5
1. It won't let you. Two options: (a) pad with something, such as NaNs, (b) use cell arrays to store each matrix in a separate cell. For (a):
X = [[l1;NaN(1,3)] l2]
2. Use the range (:) operator with a step:
y = x(20:3:end)
(Assuming "every 4th element starting from 20th" you mean 20, 23, 26, etc)
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Matt Tearle
Matt Tearle 2014-11-5
I initially had that, but then somehow decided that "every 4th element" would mean like a musical interval 4th (thinking of blocks of 4 elements, including the last one). But now that I think about it again, I'm back with you -- x(20:4:end) would make more sense.
I guess Amit can figure out his interpretation and choose accordingly :)
Amit Kumar
Amit Kumar 2014-11-6
Yup, I can figure out :) Thanks a lot Matt, Image Analyst!

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