Multiplying 2 matrices, using a for loop and storing results in a table.

Hey.

I have to multiply 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've tried to do it like this:

    X=[0.80;0]

    t=pi/18

    D=[cos(t) -sin(t); sin(t) cos(t)]

    d=D*X

    X=zeros(2,10)

    for D=10:2,

    X(D)=d;

    end

But this just writes:

    X =

    0 0 0 0 0 0 0 0 0 0
    0 0 0 0 0 0 0 0 0 0

Anders. I'm a bit lost.

[Azzi Abdelmalek]

Can you explain what means 9 times?

[Anders]

It means, that i have to multiply D by X 9 times. It would be the same as D^9*X. But i have to store all the results, in a table (2, 10). First: D*X, second: D*(D*X) Third: D*(D*(D*X) and so on.

[Anders]

I've tried to do it like this: X=[0.80;0] t=pi/18 D=[cos(t) -sin(t); sin(t) cos(t)] d=D*X X=zeros(2,10) for D=10:2, X(D)=d; end But this just writes: X = 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Answer 1

[Andrei Bobrov]

[EDIT]

X=[0.80;0];
t=pi/18;
D=[cos(t) -sin(t); sin(t) cos(t)];
X(2,10) = 0;
for jj = 2:size(X,2)
    X(:,jj) = D*X(:,jj-1);
end

[Anders]

Is this using a for loop? How do I store the results in X=zeros(2,10)?

[Anders]

I've tried to do it like this: X=[0.80;0] t=pi/18 D=[cos(t) -sin(t); sin(t) cos(t)] d=D*X X=zeros(2,10) for D=10:2, X(D)=d; end But this just writes: X = 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

[Andrei Bobrov]

corrected

[Anders]

Thank you!

Answer 2

[sixwwwwww]

Dear Andres, you can do it as follows using for loop:

D = [cos(pi/18) -sin(pi/18); sin(pi/18) cos(pi/18)];
X = [0.80;0];
result = zeros(2, 9);
for i = 1:9
    result(1, i) = D(1, 1) * X(1) + D(1, 2) * X(2);
    result(2, i) = D(2, 1) * X(1) + D(2, 2) * X(2);
end
disp(result)

I hope it helps. Good luck!

[Anders]

Thank you!