MATLAB: Building the Matrix from the two matrices

building matrix from two matricesMATLAB

Hey, I am stuck in building the Matrix for my project "Thermal Network''. The problem is how to buid the Matrix from the two matrices of same dimensions.
Details goes here;
LA = [ 0 77 0 0; 77 0 15 0; 0 15 0 0; 0 0 0 0];
LB = [ 0 0 0 25; 0 0 0 28; 0 0 0 25; 25 28 25 0];
Now I need to build the matrix L like;
L= [LA(2,1)+LB(1,4) (-LA(1,2)) 0 (-(LB(1,4));
(-LA(2,1)) LA(2,1)+LA(2,3)+LB(2,4) (-LA(2,3)) (-LB(2,4));
0 (-LA(3,2)) LA(3,2)+LB(3,4) (-LB(3,4));
(-LB(4,1)) (-LB(4,2)) (-LB(4,3)) 0];
or else like this also fine:
L= [LA(1,2)+LB(4,1) (-LA(2,1)) 0 (-(LB(4,1));
(-LA(1,2)) LA(1,2)+LA(3,2)+LB(4,2) (-LA(3,2)) (-LB(4,2));
0 (-LA(2,3)) LA(2,3)+LB(4,3) (-LB(4,3));
(-LB(1,4)) (-LB(2,4)) (-LB(3,4)) 0];
May be it would be possible using for-loop. It is just sample model, If i change the martices dimensions, Matrix should be built automatically, that's why for-loop would be better option!
If you have any suggestions and your answers are most weclomed and appreciated as well

Best Answer

Hi,
Please check the answer
LA = [     0    77      0         0; 
           77    0      15        0;
           0    15      0         0; 
           0     0      0         0];
LB = [     0     0      0      25; 
           0     0      0      28; 
           0     0      0      25;
          25    28     25      0];
[m,n ] = size(LB);
L = -LB;
L(1: m-1, 1:n-1) = -LA(1: m-1, 1:n-1);
for k = 1: m
    L(k,k) = -(sum(L(k,:)));
end
L(m,m) = 0;
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