Save New Variable to the Workspace for every iteration with a 'for' cycle

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kerozi
kerozi 2016-5-23
评论： kerozi 2016-5-24
Hello all,
I've been trying to save the Q_bar(3x3 matrix) answer seperately for every theta input but I am failing to save the Q_bar answer for each iteration. Because the only output is the final Q_bar matrix.
for theta = [0,45,60,45,45,60,45,0];
m = cos(theta*pi/180);
n = sin(theta*pi/180);
T = [m.^2 n.^2 2*m*n ; n.^2 m.^2 -2*m*n ; -m*n m*n m.^2-n.^2];
Tinv = inv(T);
Q_bar = Tinv*Q*T;
Q_bar = Q_bar(theta);
end
The final output should be Q_bar(0) = [3x3 matrix] , Q_bar(45) = [3x3 matrix], Q_bar(60) = [3x3 matrix] etc.
What can I do?
Thank You already
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kerozi
kerozi 2016-5-23
I have thought with another for loop inside should give an answer but it does not.
theta = [0,45,60,45,45,60,45,0];
for i=1:8;
m = cos(theta(i)*pi/180);
n = sin(theta(i)*pi/180);
T = [m.^2 n.^2 2*m*n ; n.^2 m.^2 -2*m*n ; -m*n m*n m.^2-n.^2];
Tinv = inv(T);
Q_bar = Tinv*Q*T;
Q_bar = Q_bar(theta(i));
end
AND I FORGOT TO TELL THAT Q MATRIX IS ALSO 3x3 MATRIX.

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采纳的回答

Stephen23
Stephen23 2016-5-23
编辑：Stephen23 2016-5-23
Exactly as Adam said in their comment, just use a 3D array like this:
Q = randi(9,3,3);
vec = [0,45,60,45,45,60,45,0];
out = NaN([size(Q),numel(vec)]);
for k = 1:numel(vec)
theta = vec(k);
m = cos(theta*pi/180);
n = sin(theta*pi/180);
T = [m.^2 n.^2 2*m*n ; n.^2 m.^2 -2*m*n ; -m*n m*n m.^2-n.^2];
Tinv = inv(T);
Q_bar = Tinv*Q*T;
out(:,:,k) = Q_bar;
%Q_bar = Q_bar(theta);
end
But note that you should use \ instead of inv.
  1 个评论
kerozi
kerozi 2016-5-24
Thank You, as much as it seems an easy task, it was hard for me to comprehend the overall. But you made it happen. Thank You so much.

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更多回答（1 个）

Steven Lord
Steven Lord 2016-5-23
You're trying to create variables like Q_bar0, Q_bar45. etc.? DON'T DO THAT. That would make your code more difficult to read and probably slower. Read this Answer for an explanation.
Adam's suggestion is the recommended approach.
theta = 0:45:360;
M = zeros(3, 3, length(theta));
for k = 1:length(theta)
T = theta(k);
M(:, :, k) = [1 0 0; 0 cosd(T) -sind(T); 0 sind(T) cosd(T)];
end
The rotation matrix for the angle theta(N) [for N between 1 and length(theta)] is M(:, :, N).
And don't use inv, use the backslash operator \ instead.

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