How do I index into a 2D matrix using two equal length R and C vectors?

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Ashish Uthama
Ashish Uthama 2011-7-7
I have a 2D matrix rho, and two vectors of indices R and C. How do I use R and C to index into rho?
>> rho=d
rho =
16 2 3 13
5 11 10 8
9 7 6 12
4 14 15 1
>> R=[1 2]; C=[ 2 3];
i.e I want to obtain rho(R(1), C(1) ..etc

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采纳的回答

Ashish Uthama
Ashish Uthama 2011-7-7
You can use a combination of linear indexing and the function sub2ind to index into rho:
>> rho=d
rho =
16 2 3 13
5 11 10 8
9 7 6 12
4 14 15 1
>> R=[1 2]; C=[ 2 3];
>> ind = sub2ind(size(rho), R, C);
>> rho(ind)
ans =
2 10

更多回答（1 个）

Sean de Wolski
Sean de Wolski 2011-7-7
Or:
rho = magic(4);
R=[1 2]; C=[ 2 3];
diag(rho(R,C))
runs much faster for smaller R,C but much longer for big ones...

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