Help in doing Matrix Multiplication

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MAHESH
MAHESH 2013-10-9
回答： sixwwwwww 2013-10-9
Dear All, I am doing Matrix Multiplication of following 3 matrices .
( A of size 24x24, B of size 1*24 and C of 1 x 24 ]
(Matrix A contains digits while Matrix B & C contains 24 variables.
but I am not succeeding in getting the answer.
A = [93 65 41 47 31 30 37 30 31 31 34 32 30 68 2 68 -8 5 11 -1 15 20 13 52;
65 55 35 39 22 26 30 26 25 24 25 24 21 53 16 61 9 4 3 -3 11 18 11 28;
41 35 34 32 17 17 23 17 19 15 16 22 16 32 14 23 16 9 4 4 13 12 17 38;
47 39 32 50 27 30 29 18 21 21 15 27 24 38 20 39 33 5 4 2 12 10 19 33;
31 22 17 27 22 21 14 7 10 9 5 12 7 7 -4 23 1 -3 -1 0 3 3 11 25;
30 26 17 30 21 29 18 11 12 14 15 21 12 21 16 53 24 -1 -3 -3 4 4 8 12;
37 30 23 29 14 18 30 23 22 21 21 26 22 41 31 51 25 19 6 2 6 6 10 7;
30 26 17 18 7 11 23 32 22 24 22 23 20 55 27 22 19 6 -5 -4 2 -2 6 -2;
31 25 19 21 10 12 22 22 40 28 18 21 11 -15 35 24 19 34 13 17 19 11 9 8;
31 24 15 21 9 14 21 24 28 39 34 39 29 65 31 26 23 32 10 6 16 10 5 1;
34 25 16 15 5 15 21 22 18 34 55 60 45 12 48 73 44 41 19 10 25 15 9 25;
32 24 22 27 12 21 26 23 21 39 60 85 65 138 62 81 58 46 18 16 28 14 22 47;
30 21 16 24 7 12 22 20 11 29 45 65 74 138 54 67 55 28 17 4 17 11 17 45;
68 53 32 38 7 21 41 55 -15 65 111 138 138 573 30 73 15 -2 14 -19 15 21 32 96;
2 16 14 20 -4 16 31 27 35 31 48 62 54 30 152 151 152 58 23 20 34 19 19 9;
68 61 23 39 23 53 51 22 24 26 73 81 67 73 151 448 159 53 20 -10 18 44 11 53;
-8 9 16 33 1 24 25 19 19 23 44 58 55 15 152 159 220 55 25 18 34 11 22 16;
5 4 9 5 -3 -1 19 6 34 32 41 46 28 -2 58 53 55 191 91 82 76 35 16 35;
11 3 4 4 -1 -3 6 -5 13 10 19 18 17 14 23 20 25 91 81 62 63 37 21 58;
-1 -3 4 2 0 -3 2 -4 17 6 10 16 4 -19 20 -10 18 82 62 67 59 22 27 56;
15 11 13 12 3 4 6 2 19 16 25 28 17 15 34 18 34 76 63 59 76 42 31 79;
20 18 12 10 3 4 6 -2 11 10 15 14 11 21 19 44 11 35 37 22 42 47 17 52;
13 11 17 19 11 8 10 6 9 5 9 22 17 32 19 11 22 16 21 27 31 17 37 73;
52 28 38 33 25 12 7 -2 8 1 25 47 45 96 9 53 16 35 58 56 79 52 73 244]
B = [P(1) P(2) P(3) P(4) P(5) P(6) P(7) P(8) P(9) P(10) P(11) P(12) P(13) P(14) P(15) P(16) P(17) P(18) P(19) P(20) P(21) P(22) P(23) P(24)]
C = [P(2) P(3) P(4) P(5) P(6) P(7) P(8) P(9) P(10) P(11) P(12) P(13) P(14) P(15) P(16) P(17) P(18) P(19) P(20) P(21) P(22) P(23) P(24) P(1)]
I want to perform A*B*C Can any body please tell me the syntax as I am new to Matlab.
  1 个评论
Jan
Jan 2013-10-9
Hint:
B = [P(1) P(2) P(3) P(4) P(5) P(6) P(7) P(8) P(9) P(10) P(11) P(12) P(13) P(14) P(15) P(16) P(17) P(18) P(19) P(20) P(21) P(22) P(23) P(24)]
or:
B = P(1:24);
The 2nd method contains less chances to insert a bug.

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回答（3 个）

ES
ES 2013-10-9
编辑：ES 2013-10-9
mathematically, to perform AXB for matrix A of dimensions m1,n1 and Matrix B of dimensions m2 and n2, n1 and m2 should be equal. In your case this condition is not satisfied.
But if you just need scalar multiplication, i.e., multiplying A(:,1) by B(1), A(:,2) by B(2) , A(:,3) by B(3) etc.. this can be done.
MAHESH
MAHESH 2013-10-9
Thank You very much sir for your kind help . But if I take C as column vector i.e if I take C', then if I try C' x B then it comes out to be (24 x 24) matrix. Later on if i multiply this product by A which is (24 x 24), then I should get the answer, but I am not getting. where I am wrong ????
sixwwwwww
sixwwwwww 2013-10-9
Mahesh you can do it using symbolic expression in MATLAB as following:
A = [93 65 41 47 31 30 37 30 31 31 34 32 30 68 2 68 -8 5 11 -1 15 20 13 52;
65 55 35 39 22 26 30 26 25 24 25 24 21 53 16 61 9 4 3 -3 11 18 11 28;
41 35 34 32 17 17 23 17 19 15 16 22 16 32 14 23 16 9 4 4 13 12 17 38;
47 39 32 50 27 30 29 18 21 21 15 27 24 38 20 39 33 5 4 2 12 10 19 33;
31 22 17 27 22 21 14 7 10 9 5 12 7 7 -4 23 1 -3 -1 0 3 3 11 25;
30 26 17 30 21 29 18 11 12 14 15 21 12 21 16 53 24 -1 -3 -3 4 4 8 12;
37 30 23 29 14 18 30 23 22 21 21 26 22 41 31 51 25 19 6 2 6 6 10 7;
30 26 17 18 7 11 23 32 22 24 22 23 20 55 27 22 19 6 -5 -4 2 -2 6 -2;
31 25 19 21 10 12 22 22 40 28 18 21 11 -15 35 24 19 34 13 17 19 11 9 8;
31 24 15 21 9 14 21 24 28 39 34 39 29 65 31 26 23 32 10 6 16 10 5 1;
34 25 16 15 5 15 21 22 18 34 55 60 45 12 48 73 44 41 19 10 25 15 9 25;
32 24 22 27 12 21 26 23 21 39 60 85 65 138 62 81 58 46 18 16 28 14 22 47;
30 21 16 24 7 12 22 20 11 29 45 65 74 138 54 67 55 28 17 4 17 11 17 45;
68 53 32 38 7 21 41 55 -15 65 111 138 138 573 30 73 15 -2 14 -19 15 21 32 96;
2 16 14 20 -4 16 31 27 35 31 48 62 54 30 152 151 152 58 23 20 34 19 19 9;
68 61 23 39 23 53 51 22 24 26 73 81 67 73 151 448 159 53 20 -10 18 44 11 53;
-8 9 16 33 1 24 25 19 19 23 44 58 55 15 152 159 220 55 25 18 34 11 22 16;
5 4 9 5 -3 -1 19 6 34 32 41 46 28 -2 58 53 55 191 91 82 76 35 16 35;
11 3 4 4 -1 -3 6 -5 13 10 19 18 17 14 23 20 25 91 81 62 63 37 21 58;
-1 -3 4 2 0 -3 2 -4 17 6 10 16 4 -19 20 -10 18 82 62 67 59 22 27 56;
15 11 13 12 3 4 6 2 19 16 25 28 17 15 34 18 34 76 63 59 76 42 31 79;
20 18 12 10 3 4 6 -2 11 10 15 14 11 21 19 44 11 35 37 22 42 47 17 52;
13 11 17 19 11 8 10 6 9 5 9 22 17 32 19 11 22 16 21 27 31 17 37 73;
52 28 38 33 25 12 7 -2 8 1 25 47 45 96 9 53 16 35 58 56 79 52 73 244];
A_sym = sym('A%d%d', [24 24]);
P = sym('P%d', [1, 24]);
B = [P(1) P(2) P(3) P(4) P(5) P(6) P(7) P(8) P(9) P(10) P(11) P(12) P(13) P(14) P(15) P(16) P(17) P(18) P(19) P(20) P(21) P(22) P(23) P(24)];
C = [P(2) P(3) P(4) P(5) P(6) P(7) P(8) P(9) P(10) P(11) P(12) P(13) P(14) P(15) P(16) P(17) P(18) P(19) P(20) P(21) P(22) P(23) P(24) P(1)]';
result = A_sym * (B * C);
result_new = subs(result, A_sym, A);
After this if you define a new B and C matrices then again use subs to replace symbols with their equivalent numeric values. Hope it will help you

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