How do I store data from a loop into a matrix or vector?

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Isa Duran 2015-7-22

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https://ww2.mathworks.cn/matlabcentral/answers/230736-how-do-i-store-data-from-a-loop-into-a-matrix-or-vector

评论： dpb 2015-7-22

Hi guys, I'm trying to save values from a loop into a matrix, but my code keeps overwrite the data from the loop.

          subplot(2,2,1)
          cl={'b.-','k.-','r.-','g.-','c.-','m.-','k.-','g.-','k.-'};
          rw=reshape(Rw(sp,hd,:)*L/(rho*g*B^2),[nfr,1]);
          nl=reshape(lambda(sp,hd,:),[nfr,1])/L;
          plot(nl,rw,cl{hd}); hold on; 
          grid on;
          title(['Added Resistance for ' num2str(u),' knots forward speed for  5 D.O.F '],'FontSize', 18)
          ylabel('{R_{aw} \cdot L / \rho g B^2}','FontSize', 18)
          xlabel('\lambda / L','FontSize', 18)
          xlim([0 1.5])
          speed=num2str(u(sp)); heading=num2str(uh(sp,hd)*180/pi);
          for i = 1:hd
          legendInfo{i} = ['Heading = ' num2str(uh(sp,i)*180/pi)]; % or whatever is appropriate
          end 
          legend(legendInfo)
          for pp = 1:hd
                  rwfff(:,pp) = rw(:,1)
          end

The rw is a 20x1 matrix and it runs for each hd, hd is 7. So I need to save each rw values into rwfff so rwfff is a 20x7 matrix. Hope it is understandable.

Thanks in advance

Isa Duran

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dpb 2015-7-22

在 MATLAB Online 中打开

rw=reshape(Rw(sp,hd,:)*L/(rho*g*B^2),[nfr,1]);
...
for pp = 1:hd
  rwfff(:,pp) = rw(:,1)
end

There's nowhere that rw is apparently dependent upon anything excepting coming from an array Rw and the indices to it aren't shown.

But, given that it is a column vector of some value based on those unknown values, there doesn't appear any reason that rwfff woudn't be an array of size(length(rw),hd) when the loop is finished.

It would be more efficient to preallocate rwfff with

rwfff=zeros(length(rw),hd);

before starting the loop but for such a small array it won't be noticeable but in the slightest. For large arrays neglecting this can become a severe bottleneck.

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