Save double vector in matrix in for loop

Question

Bruce Rogers 2021-7-2

1
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/870458-save-double-vector-in-matrix-in-for-loop

评论： Bruce Rogers 2021-7-2

Hello everyone,

I'm trying to safe the values of a variable into a matrix. The calculations happen in a for loop, but only the last iteration will be saved into the matrix. Is there an error in my code or is it just wrong how I'm trying to save the double vector into the matrix?

I'll put some part of the code below. Just tell me, if you need the whole code.

Thanks for your help!

for j = 1:5
    
%... a long code with calculations to get the phase shift of two sine
%curves
% time difference for positive slope crossing points
dt_pos_slope = t0_pos1 - t0_pos2;
% time difference for negative slope crossing points
dt_neg_slope = t0_neg1 - t0_neg2;
d_df_mat = zeros(10,5);
d_df = [dt_neg_slope dt_pos_slope]';
d_df = abs(d_df(:));
d_df_mat(:,j) = d_df;           %Here I'm trying to save the values 
                                %into the d_df_mat Matrix, but only the last iteration will be saved
end

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Yazan 2021-7-2

In each iteration, you are redefining the matrix d_df_mat and setting its values to zeros. Therefore, only the last iteration will survive. Define your matrix d_df_mat outside the loop.

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Answer 1

Matt J 2021-7-2

1
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/870458-save-double-vector-in-matrix-in-for-loop#answer_738373

编辑：Matt J 2021-7-2

在 MATLAB Online 中打开

The line,

d_df_mat = zeros(10,5);

should be prior to the loop, not inside it.

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Bruce Rogers 2021-7-2

Oh yes, you're right. Thanks for your help, I didn't notice

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Answer 2

KSSV 2021-7-2

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/870458-save-double-vector-in-matrix-in-for-loop#answer_738378

在 MATLAB Online 中打开

d_df_mat = zeros(10,5);
for j = 1:5
    
%... a long code with calculations to get the phase shift of two sine
%curves
% time difference for positive slope crossing points
dt_pos_slope = t0_pos1 - t0_pos2;
% time difference for negative slope crossing points
dt_neg_slope = t0_neg1 - t0_neg2;
d_df = [dt_neg_slope dt_pos_slope]';
d_df = abs(d_df(:));
d_df_mat(:,j) = d_df;           %Here I'm trying to save the values 
                                %into the d_df_mat Matrix, but only the last iteration will be saved
end