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Select elements of Matrix?

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Fred John
Fred John 2014-12-3
编辑： Azzi Abdelmalek 2014-12-3
Hi,
I have a 20x20 matrix, P. I wish to define a matrix Q such that the rows of Q are the LAST 18 rows of P (rows 2-20), and the columns of Q are the last 18 columns of P (columns 2-20).

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采纳的回答

Guillaume
Guillaume 2014-12-3
It's basic matrix indexing:
Q = P(2:20, 2:20)

更多回答（2 个）

C.J. Harris
C.J. Harris 2014-12-3
Like so:
P = magic(20);
Q = P(end-17:end,end-17:end);
Or this, as I assume you mean rows/columns 3 to 20 - otherwise you'll have 19 rows/columns:
P = magic(20);
Q = P(3:20,3:20);
Azzi Abdelmalek
Azzi Abdelmalek 2014-12-3
编辑：Azzi Abdelmalek 2014-12-3
P=rand(20) % Example
n=18
Q=P(end-n+1:end,end-n+1:end)

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