I know it it is possible to set a matrix's diagonal elements to a constant like this:

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Matrix<float, 100, 100> m;
m.diagonal().setConstant(9);


However, I want to set the adjacent diagonal elements to particular constants too, i.e. I want to take not the main diagonal elements but the diagonal elements where each of the elements is one position below the main diagonal. Is there a way to do it without looping?

EDIT: I have figured out one possible solution:

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m.block(1, 0, 99, 99).diagonal().setConstant(100);

Besides this, is there a "better" way to do it?

yes, mat.diagonal(-1) or mat.diagonal(1) to get the sub/super diagonals, and of course you can get the other diagonals too... See: http://eigen.tuxfamily.org/dox-devel/cl ... 3dd988a7f7