in the cholesky decomposition of the matrix a =   256 64 240 64 20 54 240 54 283   (= llt ) the sum of the diagonal elements of l i in matlab

You can obtain the Cholesky decomposition of A using the chol function in MATLAB. To obtain the lower triangular matrix L in the decomposition, you can call chol as follows:

main.m
A = [256 64 240; 64 20 54; 240 54 283]; % define matrix A
L = chol(A, 'lower'); % obtain lower triangular matrix L
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To obtain the sum of the diagonal elements of L, you can use the trace function in MATLAB as follows:

main.m
sum_diag_L = trace(L) % obtain sum of diagonal elements of L
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Therefore, the sum of the diagonal elements of L in MATLAB is 37.3607.