Creating matrix inside indexed for loop

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Luc Kuijken 2020-10-28

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评论： Luc Kuijken 2020-10-29

I would like to know how to create a matrix inside a for loop with indexing. The indexing causes an array on its own, but I already have a vector (V, U and W) inside the for loop. Now I would like to create a matrix that shows the vector at each timestamp, but it gives the error : Unable to perform assignment because the indices on the left side are not compatible with the size of the right side.

To my knowledge, using a ' ; ' inside a vector makes it jump to the next row instead of using a ' , ' to jump to the next column. That's why I used it inside the vectors V and U. Because then the time vector would jump to the next column each iteration of the for loop, leaving a nice 2 by 1002 matrix, but as said before, it gave an error

This is my code:

%% Dimensions VAWT
R = 0.5;
H = 1.5;
%% Speeds
labda = 4;
V = [0;1];
theta(1) = 0;
omega = norm(V)*labda/R;
U_magnitude = omega*R;
%% Variables
i(1) = 1;
dt = 0.01;
rotations = 0;
%% Calculation
for t = 0:dt:10
    i = i+1;
    
    theta(i) = theta(i-1) + (omega*dt);
    if theta(i) <= (2*pi)
        theta(i) = theta(i-1) + (omega*dt);
    else
        theta(i) = theta(i) - (2*pi);
        rotations = rotations+1;
    end
    
    angle_U(i) = theta(i) + (0.5*pi);
    U(i) = [cos(angle_U(i))*U_magnitude;sin(angle_U(i))*U_magnitude];
    
    W(i) = V - U(i);
end
Unable to perform assignment because the indices on the left side are not compatible with the size of the right side.
rotations = rotations + (theta(i)/(2*pi));

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Answer 1

Mathieu NOE 2020-10-29

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hi

as far as I understand U,V,W have 2 rows , so if I am right, this is the way to modifiy your code

%% Dimensions VAWT
R = 0.5;
H = 1.5;
%% Speeds
labda = 4;
V = [0;1];
theta(1) = 0;
omega = norm(V)*labda/R;
U_magnitude = omega*R;
%% Variables
i(1) = 1;
dt = 0.01;
rotations = 0;
%% Calculation
for t = 0:dt:10
    i = i+1;
    
    theta(i) = theta(i-1) + (omega*dt);
    if theta(i) <= (2*pi)
        theta(i) = theta(i-1) + (omega*dt);
    else
        theta(i) = theta(i) - (2*pi);
        rotations = rotations+1;
    end
    
    angle_U(i) = theta(i) + (0.5*pi);
    U(:,i) = [cos(angle_U(i))*U_magnitude;sin(angle_U(i))*U_magnitude];
    
    W(:,i) = V - U(:,i);
end