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Matrix multiplication and addition

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Raheema Syed
Raheema Syed 2019-2-19
回答： Star Strider 2019-2-19
suppose i have two matrices:
a= [1 0 0 2 0 6
1 0 0 2 0 7
1 0 0 2 0 8
1 0 0 2 0 9
1 0 0 2 0 10]
b= [ 1 2 3 4 5
2 3 4 5 6
3 4 5 6 7
4 5 6 7 8
5 6 7 8 9
6 7 8 9 10
7 8 9 10 11
8 9 10 11 12]
i need to consider only 6th coloumn in my 'a' matrix i.e only [6;7;8;9;10]. size of 'a' matrix will be 5x1 now. And from 'b' matrix only 1st fours rows need to be considered. New size of 'b' matrix will be 4x5. Then, the following operation needs to be done between new 'a' and new 'b' matrix:
r= 6x1+7x2+8x3+9x4+10x5
s=6x2+7x3+8x4+9x5+10x6
t=6x3+7x4+8x5+9x6+10x7
u=6x4+7x5+8x6+9x7+10x8
sum=r+s+t+u
How should the matlab code be written for the above operation?

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回答（2 个）

Kevin Phung
Kevin Phung 2019-2-19
m1 = a(:,6);
m2 = b(1:4,:)';
prod = m1.*m2;
part_sums = sum(prod);
r = part_sums(1);
s = part_sums(2);
t = part_sums(3);
u = part_sums(4);
total_sum = r + s + t + u;
% or you can just do sum(sum(prod)) and skip the r s t u
Star Strider
Star Strider 2019-2-19
If I understand correctly what you want to do, this works:
Result = sum(b(1:4,:) * a(:,6));
producing:
Result =
760

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