Inner Matrix Dimensions Must Agree

I have a matrix of 119 x 1 and Z is 119 x 119

should multiply it by a diagonal matrix of 2 x 2:

W = [0.12  0 ;
     0     0.28];
d=sqrt(W*X'*Z*X*W);

I am receiving an error which is:

Inner Matrix Must agree!!

Please, any suggestion?

Answer 1

[Image Analyst]

That can never work. If all you have is dimensions of 119 and 1, then there is no way you can do anything to get 2 rows or 2 columns, no matter what you do or how you manipulate (transpose) them. The result will always have dimensions of 119 and/or 1 - never 2. Therefore, you will never be able to right multiply, or left multiply, by a 2-by-2 matrix W.

[shawin]

If we move row by row, what I mean multiply each row by a 2x2 matrix ?

[Image Analyst]

A row is a 1-by-N array, and that cannot be multiplied by a 2-by-2 matrix. If you have two matrices, an a-by-b called m1, and a c-by-d matrix called m2, then to do m1*m2 you must have b equal c, and if you do m2*m1 you must have d equal a. That's just basic matrix algebra rules.

Answer 2

[KALYAN ACHARJYA]

• Matrix multiplication rows of the first matrix should be equal columns of the second matrix
• you have considering one matrix is 2x2 order, how can you do the multiplication with 1x119 or 119x119

x=rand(119,1); )%Order 119x1
z=rand(119,119); %Order 119x119
w=[0.12 0; 0 0.28]; %Order 2x2
%x' order 1x119
d=sqrt(w.*x'*z.*x.*w); %This does not work, check the order of all Matrixes

Learn Matrix multiplication here

[Image Analyst]

That does not work.

[KALYAN ACHARJYA]

@Image Analyst yes sir it does not work

[Stephen23]

"Matrix multiplication rows of the first matrix should be equal columns of the second matrix or vice versa"

The number of columns of the first matrix must be equal to the number of rows of the second matrix. There is certainly no "vice versa" involved.

[KALYAN ACHARJYA]

Yes @Stephen Cobeldick, Thanks for pointing the error