Vector and Matrix mutiplication

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Moe Joe 2016-11-27

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评论： Star Strider 2016-11-27

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Hi there;

I have a vector A(kx1) and a matrix B (nxk). I need select rows from that correspond to ONES in A, and sum those rows mod2:

Example:

 A =[1     0     1     0     1] and 
 B = [1     0     1     0     1;
     1     0     0     1     0;
     0     1     1     1     1;
     1     1     0     1     1;
     0     1     1     0     1];

In this example, I want to add rows that indicates ones in A, i.e. rows of B(1, 3,5) & sum those 3 rows mod2.

Kindly help.

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Star Strider 2016-11-27

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I’m not certain that I understand what you want to do.

See if this works:

A = [1 0 1 0 1];
B = [1 0 1 0 1; 1 0 0 1 0; 0 1 1 1 1; 1 1 0 1 1; 0 1 1 0 1];
C = B(logical(A'),:);
Out = mod(sum(C,2),2)

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Moe Joe 2016-11-27

question.png

OK, let me rephrase my question in terms of a picture:

Star Strider 2016-11-27

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That clarifies things. You are actually summing the columns of ‘D’, so that would be ‘sum(D,1)’ (or more simply, ‘sum(D)’) rather than ‘sum(D,2)’ that would sum the rows.

So the desired result would be:

Out = mod(sum(D),2)

or in my code:

Out = mod(sum(C),2)

producing the result described by (5).

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