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P=eye(4,4)

gives

P =
1000
0100
0010
0001

• The matrix of size (n ⊗ n) with elements randomly chosen from
the interval [0, 1], such as:

Q=rand(4,4)

gives, in one instance:

Q =
0.9708 0.4983 0.9601 0.2679
0.9901 0.2140 0.7266 0.4399
0.7889 0.6435 0.4120 0.9334
0.4387 0.3200 0.7446 0.6833

• We can select to extract the upper triangular part of the Q matrix,
but assign to all the lower triangle elements the value zero:

upQ=triu(Q)

produces

upQ =
0.9708 0.4983 0.9601 0.2679
0 0.2140 0.7266 0.4399
0 0 0.4120 0.9334
0 0 0 0.6833

or extract the lower triangular part of the Q matrix, but assign to all the upper
triangle elements the value zero:

loQ=tril(Q)

produces

loQ =

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