How to arrange vectors 3x1 after "if" code in common vector 3*ix1?

Question

D.Chehov 2012-2-29

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/30667-how-to-arrange-vectors-3x1-after-if-code-in-common-vector-3-ix1

Hello, I would like to aks you a question,probably a simple one, but which hinders me. I have this code: ----------------------------------------

for i=1:NUI;

if (i==1);
   statement.....
    elseif (i>=2 && i<=NUI-1)
       ugvg=[Ugd(3,i);Vgd(3,i);0];
        Kugvg=zeros(3,1);
        Kugvg=K*ugvg;
    elseif (i==NUI);
        statement....
  end;
end;
-----------------------------------------------------------
where Ugd and Vgd are global variables;
K is a matrix [3x3]; ugvg is a vector [3x1] and Kugvg is a resultant vector of the multiplication.
I'd like to create vector (array) whit dimensin 3*i x 1, which consecutively contains all small vectors Kugvg[3x1] for i=2:NUI-1.
Thanks in advance!
Regards

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Answer 1

Jan 2012-2-29

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https://ww2.mathworks.cn/matlabcentral/answers/30667-how-to-arrange-vectors-3x1-after-if-code-in-common-vector-3-ix1#answer_39124

在 MATLAB Online 中打开

Kugvg = zeros(3, NUI);  % Pre-allocation
iK    = 0;
for i = 1:NUI
  if i==1
    statement.....
  elseif i <= NUI-1  % i is always >= 2, if i==1 is checked before
     ugvg=[Ugd(3,i);Vgd(3,i);0];
     % Kugvg=zeros(3,1);  Not useful here!
     iK = iK + 1;
     Kugvg(:, iK) = K*ugvg;
  else  % if i==NUI, check not required!
     statement....
  end
end
% Crop and reshape to [3*i x 1]:
Kugvg = Kugvg(:, 1:iK);
Kugvg = Kugvg(:);

Instead of the coarse pre-allcation with the full number of columns, you could do this:

Kugvg = zeros(3, NUI-2);
...
        Kugvg(:, i-1) = K*ugvg;
...
% Then no cropping is required

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Answer 2

D.Chehov 2012-2-29

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/30667-how-to-arrange-vectors-3x1-after-if-code-in-common-vector-3-ix1#answer_39137

在 MATLAB Online 中打开

Dear, Jan, thank you for your kind answer,but unfortunatelly I could not use it to obtain what I need. To be more clear, I prepared this example: ----------------------------------------------------------

function example

% F is a load N1

F=[0.0000103;1523.6563491;0.0003875;-0.0000403;-0.1044340;0.0000601;-0.0000759;-0.1959430;0.0000498;-0.0000990;-0.2559150;0.0000404;-0.0001120;734.2502860;0.0003466];

Ugd=[5.1221E-5 4.6382E-5 4.1544E-5 3.6705E-5 3.1866E-5]; % displacement time history

Vgd=[0.0039514 0.0039482 0.0039449 0.0039417 0.0039385]; % velocity time history

 K=[0 0 0;
    341 540 0;
    0 0 0];

for i=1:5

    ugvg=[ Ugd(i);Vgd(i);0];
    Kugvg = K*ugvg; % K is the Load2
end;

Load=F+Kugvg; %Load=Load1+Load2 disp (Load); --------------------------------------------------------------- The error is that tha matrix dimension don't agree, becouse F is[15x1], and Kugvg is 5 small vectors [3x1]. What I need is to unify it". I tried with all my knowledge but I guess that,because of the loop iteration "for-end" I could not manage.....

Thank you again for your kind help!