Matrix Multiplication of different size

Hello,

i have 2 matrix of different size

how can i multiply

one is 2 * 2 and other is 103 * 1

so how can i do it

attached below both files

[John D'Errico]

You need to decide what it means to you to do that multiplication. A matrix multiply has a well defined meaning in mathematics, one that makes certain requirements on the allowed sizes of the matrices. Sicne your matrices do not conform for such a multiplication, only you know what you might intend for that product to involve. So only you can explain what is your goal here.

[OriAlpha]

i am preforming the roatation of the points so i have to perform multiplication

[John D'Errico]

But rotation of what points? I presume the 2x2 matrix is problably a rotation matrix from your statement. That is, it probably looks vaguely like this:

R = [cos(theta), -sin(theta) ; sin(theta), cos(theta)]

So applied to a pair of numbers [x;y] as a matrix multiply, it will rotate a point in the (x,y) plane. Thus we might have:

R = @(theta) [cosd(theta), -sind(theta) ; sind(theta), cosd(theta)];
R(45)*[1;0]
ans =
         0.707106781186547
         0.707106781186547

No problem. We mapped the point [1,0] into the new point [sqrt(2),sqrt(2)], as a 45 degree rotation. As such, this is a well defined operation.

However, you then apparently wish to apply that to a 103x1 vector. I'm sorry, but this part makes no sense in context of what you have stated as your goal.

Even if we decided that each consecutive pair of numbers is x(1), then y(1), x(2), y(2), etc., you have an odd number of elements in that vector. So rotation makes no sense in terms of what you have stated. You need to explain, CLEARLY, what rotation is to be performed, and what it means.

Answer 1

[madhan ravi]

load R.mat
load data.mat
data         *   (R(:)).'    % matrix multiplication rules
 %^---103 by 1      ^-------- 1 by 4
  %The final matrix size after multiplication will be 103 by 4