Can somebody help me get this to work in a loop???

Question

mark 2013-11-28

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回答： Walter Roberson 2013-11-29

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I'm trying to solve momentum transfer for a range of data. The basis of the script is:

Output a value as the phase angle (Th_D) shifts from 0 to 360
This, along with some other data, is solved using the simultaneous operator solve( ) ( 2 equations so 2 outputs )
The 2 outputs from solve are placed into a separate matrix that I can manipulate later

Or, to place it into steps:

Calculate the value of Veff at phase angle Th_D (store the output in a matrix)
From a specified value of Veff ( 2nd value in every column) substitute it into solve( )
solve() will output this value and store it in B1 and B2
k is increased and the loop restarts
New value of phase angle is used to compute Veff.. etc

I can get the script to work with just one value but I've been struggling for the past 3 hours to get it to work in a loop.

      A=5E-6; % amplitude
      Freq=20000;
      w=Freq*2*pi; % angular frequency
      Th_D=(0:1:360);
      th=(Th_D .* (pi/180)); % phase angle radian
      t=[0:2E-7:7.2E-5]; % time
for k=1:length(th)
Vt=-A*w;
Veff(k,:)=Vt.*sin(w.*t + th(k)); % Horn tip velocity
Vx=Veff(:,2);
   Ue=Vx;
   Uf=0;
   Meff=10;
   Mfr=20;
syms Ve Vf
B(k)=solve(Meff.*Ue(:,k) + Mfr*Uf==Meff*Ve + Mfr*Vf,...
        Meff.*Ue(:,k).^2 + Mfr*Uf^2==Meff*Ve^2 + Mfr*Vf^2);
B1(k)=B(k).Ve; % effective mass output
B1_M(k)=double(B1);
B2(k)=B(k).Vf; % free mass output
B2_M(k)=double(B2);
end

Any help would be appreciated!!!

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Answer 1

Walter Roberson 2013-11-29

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/107973-can-somebody-help-me-get-this-to-work-in-a-loop#answer_116689

在 MATLAB Online 中打开

You have

Vx = Veff(:,2)

which selects a single column out of Veff and writes it to Vx, so Vx will be a single column.

You then have

Ue = Vx

so Ue will have a single column.

You then attempt to access Ue(:,k) . That can only work if k is 1: as soon as k gets to 2, you would be attempting to access column 2 of something that only has one column.