Using 3x3 matrix to create 21x21 matrix
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Maria Galle
am 11 Nov. 2019
Kommentiert: Maria Galle
am 11 Nov. 2019
I have built a 3x3 matrix using the code below
EA = 1;
h = 1;
F = @(xi)(xi-0.5).*(xi-0.5)
k(1,1) =EA/h* 2*quad(F, -1, 1)
F = @(xi)(xi-0.5).*(-2*xi)
k(1,2) = EA/h* 2*quad(F, -1, 1)
F = @(xi)(xi-0.5).*(xi+0.5)
k(1,3) = EA/h* 2*quad(F, -1, 1)
F = @(xi)(-2*xi).*(-2*xi)
k(2,2) =EA/h* 2*quad(F, -1, 1)
F = @(xi)(xi+0.5).*(-2*xi)
k(2,3) = EA/h*2*quad(F, -1, 1)
F = @(xi)(xi+0.5).*(xi+0.5)
k(3,3) = EA/h*2*quad(F, -1, 1)
k(2,1) = k(1,2)
k(3,1) = k(1,3)
k(3,2) = k(2,3)
I want to use the 3x3 matrix above to create a 21x21 matrix following the pattern below
![new doc 2019-11-11 00.20.06_1.jpg](https://www.mathworks.com/matlabcentral/answers/uploaded_files/247693/new%20doc%202019-11-11%2000.20.06_1.jpeg)
the overlapped elements should be added together, the numbers not in the 3x3 matrix are zero in the bigger matrix...k(4,1)=0 etc..
10 3x3 matrices should be used
I want to use a for loop unless there's another method
1 Kommentar
Walter Roberson
am 11 Nov. 2019
This was recently discussed in https://www.mathworks.com/matlabcentral/answers/489626-adding-matrices-to-make-bigger-matrix
It is a lot easier and clearer to loop building up the matrix, at least in the case where the different matrices on the diagonal are different.
Akzeptierte Antwort
Erivelton Gualter
am 11 Nov. 2019
It is not clear the overlap values. I assumed the following:
- k33+k11
- k33+k12
- K33+k13
- K33+k23
- ..., Until the last is k33+k33
The other values is just copy from the given location. Then, you might use only for loop for this. Check in the following:
k19 = reshape(k(1:3,1:3),1,9); % Reshape for [k11 k12 k12 k21 k22 k23 k31 k32 k33]
j = 1;
for i=4:2:21
k(i,i-1) = k(2,1);
k(i-1,i) = k(2,1);
k(i+1,i-1) = k(3,1);
k(i-1,i+1) = k(3,1);
k(i+1,i) = k(3,2);
k(i,i+1) = k(3,2);
k(i,i) = k(2,2);
k(i+1,i+1) = k(3,3) + k19(j); % Overlap goes here
j = j + 1;
end
3 Kommentare
Erivelton Gualter
am 11 Nov. 2019
Can you rephrase what is the values for k(3,3), k(5,5), k(7,7), ...
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