Asked by Maria Galle
on 11 Nov 2019 at 3:48

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

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

Answer by Erivelton Gualter
on 11 Nov 2019 at 4:42

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

Maria Galle
on 11 Nov 2019 at 5:16

the last value k(21,21) should equal k(3,3)

Erivelton Gualter
on 11 Nov 2019 at 15:23

Can you rephrase what is the values for k(3,3), k(5,5), k(7,7), ...

Maria Galle
on 11 Nov 2019 at 16:30

k(3,3)=k(3,3)+k(1,1)

EA = 1;

h = 1;

F = @(xi)(xi+0.5).*(xi+0.5)

k(3,3) = EA/h*2*quad(F, -1, 1)

F = @(xi)(xi-0.5).*(xi-0.5)

k(1,1) =EA/h* 2*quad(F, -1, 1)

this equals k(5,5) and k(7,7)...

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## Walter Roberson (view profile)

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