Find and assign values in matrix

Question

Simon Kibsgaard 2020-12-3

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/676563-find-and-assign-values-in-matrix

回答： Anmol Dhiman 2020-12-9

for n = 1:40 % loop over nodes with load
    triNodes = qTop(n,:);  % nodes of the considered triangle
    triDof = globDof(triNodes,:)';  % degrees of freedom in global system
    triCoord = nodeCoord(triNodes,1:nDim)  % coordinates of triangle nodes
    triCross(n,:) = cross((triCoord(1,:))-(triCoord(2,:)),(triCoord(1,:))-(triCoord(3,:)));
    triAre(n,:) = (norm(triCross(n,:))/2) ;
    q3(n,:)=[qTop(n,1) qTop(n,2) qTop(n,3) triAre(n,:)]
end 
 

I have this code which produces the following output:

q3 =
0000    2.0000   90.0000    4.9424
0000    3.0000   91.0000    4.3018
0000    4.0000   92.0000    3.7912
0000    5.0000   93.0000    3.4618
0000    6.0000   94.0000    3.3465
0000    7.0000   95.0000    3.4566
0000    8.0000   96.0000    3.7815
0000    9.0000   97.0000    4.2892
0000   10.0000   98.0000    4.9293
0000   11.0000   99.0000    5.6382
    ...

Now i would lige to assign 1/3 of the value in the 4th column to each of the nodenumbers in the 1st, 2nd and 3rd column.

Thereafter i would like the sum of all values assigned to eachnode to be displayed besides the node in a 10x2 matrix.

Hope you can help, thanks in advance :)

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dpb 2020-12-3

Illustrate, don't just talk... :)

Give us the expected output from the above input.

Simon Kibsgaard 2020-12-3

编辑：Simon Kibsgaard 2020-12-3

在 MATLAB Online 中打开

Of course

I'd like the output to be like this:

0000    (4.9424/3)
0000    (4.9424/3)+(4.3018/3)
0000    (4.3018/3)+(3.7912/3)
0000    (3.7912/3)+(3.4618/3)
0000    (3.4618/3)+(3.3465/3)
0000    (3.3465/3)+(3.4566/3)
    ... 
0000   (4.9293/3)
0000   (5.6382/3)
    

My dataset is much bigger than these 10 lines, otherwise it could have been done by hand.

Thanks for the help, it is very appereciated

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Answer 1

Anmol Dhiman 2020-12-9

0
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https://ww2.mathworks.cn/matlabcentral/answers/676563-find-and-assign-values-in-matrix#answer_569864

在 MATLAB Online 中打开

Hi Simon,

Assuming your result stored in output (variable). follow the below code

areaIndex = output(:,4)/3;
finalOutput = zeros(100,2) % assuming number of nodes is 100
for i = 1:100
    idx1 = find(output(:,1)==i);
    idx2 = find(output(:,2)==i);
    idx3 = find(output(:,3)==i);
    sumArea = areaIndex(idx1) + areaIndex(idx2) + areaIndex(idx3);
    finalOutput = [i sumArea];
end