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I have compiled lists of non-diagonal and diagonal entries for a matrix. I'm trying to add elements from the diagonal-entry lists into certain entries of the non-diagonal lists. Is there a feasible way I can add these lists without retyping everything up in a new list? Or should I just try another approach?

I've listed examples of my lists in a much shortened version for simplicity; in reality, I'm trying to create a matrix of size 30x30. I've tried messing around with the Part[] function, but haven't been able to get it to work the way I desire.

non-diags = {{0,0,-1},{0,0,-1},{-1,-1,0}}
diags = {5,4,6}

My desired list is:

matrixlist = {{5,0,-1},{0,4,-1},{-1,-1,6}}

Thanks for any help with this!

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nondiags = {{0, 0, -1}, {0, 0, -1}, {-1, -1, 0}};
diags = {5, 4, 6};
DiagonalMatrix[diags] + nondiags

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