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Multiply parts of matrices

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Tiffany
Tiffany 2011-11-30
Hello everyone - many thanks for taking the time to read this.
Matrix A is 63x63 and Matrix B is 63x7
I want to multiply every 9x9 of Matrix A with every 9x1 of Matrix B.
So the first:
9x9 in matrix A with the first 9x1 in Matrix B
1 2 3 4 5 6 7 8 9 1
1 2 3 4 5 6 7 8 9 2
1 2 3 4 5 6 7 8 9 3
1 2 3 4 5 6 7 8 9 4
1 2 3 4 5 6 7 8 9 5
1 2 3 4 5 6 7 8 9 6
1 2 3 4 5 6 7 8 9 7
1 2 3 4 5 6 7 8 9 8
1 2 3 4 5 6 7 8 9 9
Then the second 9x9 to the right in matrix A with the second 9x1 in matrix B.
I'm currently doing it using cells which is great but need to be able to do it outside of cell format.
What would you recommend?
  2 个评论
Sean de Wolski
Sean de Wolski 2011-12-1
What's wrong with using cells?
Tiffany
Tiffany 2011-12-1
Absolutely nothing but this has to go in part of a loop where using cells has proved to be very difficult.

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采纳的回答

Andrei Bobrov
Andrei Bobrov 2011-12-1
variant 1
A = randi(100,8,6);
B = randi(50,4,3);
[m n] = size(A);
q = 4;
p = 2;
a1 = reshape(permute(reshape(A,q,m/q,p,[]),[1 3 2 4]),q,p,[]);
out = reshape(sum(bsxfun(@times,a1,reshape(B,1,p,[])),2),m,[]);

更多回答（1 个）

Walter Roberson
Walter Roberson 2011-11-30
When you say multiply the 9x9 by the 9x1, is that a matrix multiplication (which would output a 9x1), or is that an element-by-element multiplication producing 9 x 9 with each row in A multiplied the (single) value from the corresponding column in B ?
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Tiffany
Tiffany 2011-12-1
Brill, I'll check that out. Thanks!
Walter Roberson
Walter Roberson 2011-12-1
Correction:
Bcol = 1 + (block_struct.location(2) - 1)/9

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