使用for循环在Matlab中进行矩阵乘法

Question

I have to multiply D=[cos(pi/18) -sin(pi/18); sin(pi/18) cos(pi/18)] D=[cos(pi/18) -sin(pi/18); sin(pi/18) cos(pi/18)] by X= [0.80;0] 9 times, using a for loop. I want to store the results in a table of the form: X=zeros(2,10)

I'm a bit lost.

Anders.

Answer 1

Your question is not very clear. Looping D*X ( 2x1 matrix) 9 times doesn't give you 2x10 matrix.

Is this what you're looking for?

D = [cos(pi/18) -sin(pi/18); sin(pi/18) cos(pi/18)];
X = [0.80;0];
O = ones(1,9);
A = D*X*O

Output:

A =

 Columns 1 through 8:

   0.78785   0.78785   0.78785   0.78785   0.78785   0.78785   0.78785   0.78785
   0.13892   0.13892   0.13892   0.13892   0.13892   0.13892   0.13892   0.13892

 Column 9:

   0.78785
   0.13892

Note : Matrix manipulations don't need loop in Matlab most of the times

Answer 2

IF the result of @jkshah's answer is what you want, use his answer (maybe change the O matrix to O = ones(1,10) ). The reason MatLab is named like this is because it (or she :p ) is great with matrix operations and if you can you better avoid loops. In case you want to work with loops this is a way to do it:

D = [cos(pi/18) -sin(pi/18); sin(pi/18) cos(pi/18)]; % Input
X = [0.80;0];                                        % Input
A = D*X;                                             % The function
X = zeros(2,10);                                     % Initialize the result table

X(:,1)=A;                                            % Insert the result in 
                                                     % the first column

for i =1:9                                           % Iterate to fill the 2X10 table
    X(:,i+1) = A;
end