subdiagonal
Represents the subdiagonal in a matrix.
Syntax

subdiagonal(A)

A
is a matrix

The returned value is an lvalue.
Description
If A
is a matrix, not necessarily square, then subdiagonal(A)
represents the subdiagonal in A
, that is, the entries A[i, j]
where i = j + 1
.
Typewise, subdiagonal(A)
is a vector.
subdiagonal(A)
is an lvalue, so it may be assigned to. If A
is a real matrix, then only a real vector can be assigned to it.
Examples
A ≔ ❨❨1, 2, 3❩, ❨5, 1, 2❩, ❨6, 6, 5❩, ❨4, 2, 1❩❩
⎛1 2 3⎞ ⎜5 1 2⎟ ⎜6 6 5⎟ ⎝4 2 1⎠
subdiagonal(A)
⎛5⎞ e⎜6⎟ ⎝1⎠
subdiagonal(A) ≔ ❨3, 9, 4❩
⎛3⎞ e⎜9⎟ ⎝4⎠
A
⎛1 2 3⎞ ⎜3 1 2⎟ ⎜6 9 5⎟ ⎝4 2 4⎠