I am trying to make a new matrix for each iteration of a for loop

Question

Kiernan O'Boyle 2022-4-27

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1706475-i-am-trying-to-make-a-new-matrix-for-each-iteration-of-a-for-loop

评论： Stephen23 2022-4-27

I am not sure how to make a new matrix for each iteration, I would like to have Q_bar1, Q_bar2, Q_bar3, Q_bar4 each having differnt values. I know I need to initalize if I am using Q_bar(i) but I am not sure how to do that.

%% Making Qbar matrices for all thetas

for i = 1:length(theta)

m = cosd(theta(i));

n = sind(theta(i));

T1 = [m^2, n^2, 2*n*m

n^2, m^2, -2*n*m

-n*m, n*m, (m^2)-(n^2)];

T2 = [m^2, n^2, n*m

n^2, m^2, -n*m

-2*n*m, 2*n*m, (m^2)-(n^2)];

Q_bar(i)= inv(T1)*Q*T2;

end

ERROR MESSAGE:

Unable to perform assignment because the indices on the left side are not compatible with the

size of the right side.

Error in project2 (line 85)

Q_bar(i)= inv(T1)*Q*T2;

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Stephen23 2022-4-27

在 MATLAB Online 中打开

You should replace this

inv(T1) * Q * T2

with the more efficient and numerically more robust

T1 \ Q * T2

See: https://www.mathworks.com/help/matlab/ref/inv.html#bu8tv8c-6

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Answer 1

Jan 2022-4-27

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1706475-i-am-trying-to-make-a-new-matrix-for-each-iteration-of-a-for-loop#answer_952255

编辑：Jan 2022-4-27

在 MATLAB Online 中打开

Q_bar = cell(1, length(theta));
for i = 1:length(theta)
    m = cosd(theta(i));
    n = sind(theta(i));
    T1 = [m^2, n^2, 2*n*m; ...
          n^2, m^2, -2*n*m; ...
         -n*m, n*m, m^2 - n^2];
    T2 = [m^2, n^2, n*m; ...
          n^2, m^2, -n*m: ...
         -2*n*m, 2*n*m, m^2 - n^2];
    Q_bar{i} = inv(T1) * Q * T2;
end

Or alterntively:

Q_bar = zeros(3, 3, length(theta));
for i = 1:length(theta)
    m = cosd(theta(i));
    n = sind(theta(i));
    T1 = [m^2, n^2, 2*n*m; ...
          n^2, m^2, -2*n*m; ...
         -n*m, n*m, m^2 - n^2];
    T2 = [m^2, n^2, n*m; ...
          n^2, m^2, -n*m: ...
         -2*n*m, 2*n*m, m^2 - n^2];
    Q_bar(:, :, i) = inv(T1) * Q * T2;
end