... 2; -1 3 4; -2 -1 3],bythecommand L1=tril(A) we obtainL1 =300 -1 30 -2 -1 3while, by L2=tril(A,1), we obtainL2 =310 -1 34 -2 -1 3Texts inComputational Scienceand Engineering2EditorsTimothy ... triu(A,m), with m ranging from -n and n, allowthe extraction of the triangular part augmented by, or deprived of, mextradiagonals.For instance, given the matrix A =[3 1 2; -1 3 4; -2 -1 3],bythecommand ... . . . . . . . . . . . . . . . . . . . . . . . 2348 Numerical methods for (initial-)boundary-valueproblems 2378.1 Approximation of boundary-value problems . . . . . . . . . . . . 2408.1.1 Approximation...