MATLAB: Hello, does anybody know why matlab show this error for the line of “Kg(i)” ? error : Subscripted assignment dimension mismatch. (I appreciate if you help me.)

subscripted assignment dimension mismatch

XY=[0 0;0 3.5;0 0;4 0;0 0;4 3.5;0 3.5;4 0;0 3.5;4 3.5;4 3.5;4 0] , elementnumber=6 , A=1 , E=1
for i=1:elementnumber;
    L(i)=sqrt((XY(2*i,1)-XY(2*i-1,1))^2+((XY(2*i,2)-XY(2*i-1,2))^2))
    theta(i)=atan((XY(2*i,2)-XY(2*i-1,2))/(XY(2*i,1)-XY(2*i-1,1)))*180/pi
    c(i)=cosd(theta(i))
    s(i)=sind(theta(i))
    Kg(i)=A*E/L(i)*[c(i)^2 c(i)*s(i) -c(i)^2 -c(i)*s(i);c(i)*s(i) s(i)^2 -c(i)*s(i) -s(i)^2;-c(i)^2 -c(i)*s(i) c(i)^2 c(i)*s(i);-c(i)*s(i) -s(i)^2 c(i)*s(i) s(i)^2]
end

Best Answer

Your ‘Kg’ calculation creates a new (4x4) matrix in each iteration. Subscript it as:

Kg(:,:,i) = A*E/L(i)*[c(i)^2 c(i)*s(i) -c(i)^2 -c(i)*s(i);c(i)*s(i) s(i)^2 -c(i)*s(i) -s(i)^2;-c(i)^2 -c(i)*s(i) c(i)^2 c(i)*s(i);-c(i)*s(i) -s(i)^2 c(i)*s(i) s(i)^2]

and the error disappears.

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MATLAB: How to assemble Kglobal in a for loop

for (i = 1:nelement)

Remove the parentheses.

      theta = connectivity_data(i,4);
      C = cosd(theta);
      S = sind(theta);
      U = [C.^2 C.*S -C.^2 -C.*S;
          C.*S S.^2 -C.*S -S.^2;
          -C.^2 -C.*S C.^2 C.*S;
          -C.*S -S.^2 C.*S S.^2 ];
      L = connectivity_data(i,5);
      K = ((EA)/L)*U;
      KG(index,1) = K(1,1);

Where in this loop does the variable index change its value? Did you mean to use i instead of index in determining the element in KG into which to write K(1, 1)?

end

MATLAB: Hello. I am new to matlab and I have this problem. I need to store 91 different 3×3 matrices. Yet I get this error ‘Subscripted assignment dimension mismatch.’ Can someone help me out. Many thanks

You could store them in a 3D array like this:

T = zeros(3,3,numel(thetha));  % pre-allocate outside the loop
     :
T(:,:,i) = [c(i)...etc

Then downstream in your code when you want to use the i'th 3x3 matrix you simply use the syntax T(:,:,i)

What you are currently doing doesn't work because you can't stuff a 3x3 matrix into a 1x1 spot of T.

Best Answer

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MATLAB: How to assemble Kglobal in a for loop

MATLAB: Hello. I am new to matlab and I have this problem. I need to store 91 different 3×3 matrices. Yet I get this error ‘Subscripted assignment dimension mismatch.’ Can someone help me out. Many thanks

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